Publications (46)244.53 Total impact
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Dataset: Planta Cover Image
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Article: Medicago glucosyltransferase UGT72L1: potential roles in proanthocyanidin biosynthesis.
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ABSTRACT: In the first reaction specific for proanthocyanidin (PA) biosynthesis in Arabidopsis thaliana and Medicago truncatula, anthocyanidin reductase (ANR) converts cyanidin to (-)-epicatechin. The glucosyltransferase UGT72L1 catalyzes formation of epicatechin 3'-O-glucoside (E3'OG), the preferred substrate for MATE transporters implicated in PA biosynthesis in both species. The mechanism of PA polymerization is still unclear, but may involve the laccase-like polyphenol oxidase TRANSPARENT TESTA 10 (TT10). We have employed a combination of cell biological, biochemical and genetic approaches to evaluate this PA pathway model. The promoter regions of UGT72L1 and MtANR share common cis-acting elements and direct overlapping, but partially distinct, expression patterns. UGT72L1 and MtANR are localized in the cytosol, whereas TT10 is localized to the vacuole. Over-expression of UGT72L1 in M. truncatula hairy roots results in increased accumulation of PA-like compounds, and loss of function of UGT72L1 partially reduces epicatechin, E3'OG and extractable PA levels in M. truncatula seeds. Expression of UGT72L1 in A. thaliana leads to a massive increase in E3'OG in immature seed, but reduced levels of extractable PAs. However, when UGT72L1 was expressed in the Arabidopsis tt10 mutant, extractable PA levels increased and seed coat browning was delayed. Our results suggest that glycosylation of epicatechin is important for both PA precursor transport and assembly, but that additional redundant pathways may exist.Planta 04/2013; · 3.00 Impact Factor -
Article: Establishment of the Lotus japonicus Gene Expression Atlas (LjGEA) and its use to explore legume seed maturation.
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ABSTRACT: Lotus japonicus is a model species for legume genomics. To accelerate legume functional genomics, we developed a Lotus japonicus Gene Expression Atlas (LjGEA), which provides a global view of gene expression in all organ systems of this species, including roots, nodules, stems, petioles, leaves, flowers, pods and seeds. Time-series data covering multiple stages of developing pod and seed are included in the LjGEA. In addition, previously published L. japonicus Affymetrix data are included in the database, making it a 'one-stop shop' for transcriptome analysis of this species. The LjGEA web server (http://ljgea.noble.org/) enables flexible, multi-faceted analyses of the transcriptome. Transcript data may be accessed using the Affymetrix probe identification number, DNA sequence, gene name, functional description in natural language, and GO and KEGG annotation terms. Genes may be discovered through co-expression or differential expression analysis. Users may select a subset of experiments and visualize and compare expression profiles of multiple genes simultaneously. Data may be downloaded in a tabular form compatible with common analytical and visualization software. To illustrate the power of LjGEA, we explored the transcriptome of developing seeds. Genes represented by 36 474 probe sets were expressed at some stage during seed development, and almost half of these genes displayed differential expression during development. Among the latter were 624 transcription factor genes, some of which are orthologs of transcription factor genes that are known to regulate seed development in other species, while most are novel and represent attractive targets for reverse genetics approaches to determine their roles in this important organ.The Plant Journal 03/2013; · 6.16 Impact Factor -
Article: Development of an integrated transcript sequence database and a gene expression atlas for gene discovery and analysis in switchgrass (Panicum virgatum L.).
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ABSTRACT: Switchgrass (P. virgatum L.) is a perennial C4 grass with potential to become a major bioenergy crop. To help realize this potential, a set of RNA-based resources were developed. Expressed sequence tags (ESTs) were generated from two tetraploid switchgrass genotypes, Alamo AP13 and Summer VS16. Over 11.5 million high-quality ESTs were generated with 454 sequencing technology and an additional 169,079 Sanger sequences were obtained from the 5' and 3' ends of 93,312 clones from normalized, full-length-enriched cDNA libraries. AP13 and VS16 ESTs were assembled into 77,854 and 30,524 unique transcripts (unitranscripts), respectively, using the Newbler and PAVE programs. Published Sanger-ESTs (544,225) from Alamo, Kanlow, and 15 other cultivars were integrated with the AP13 and VS16 assemblies to create a universal switchgrass gene index (PviUT1.2) with 128,058 unitranscripts, which were annotated for function. An Affymetrix cDNA microarray chip (Pvi_cDNAa520831) containing 122,973 probe sets was designed from PviUT1.2 sequences, and used to develop a Gene Expression Atlas for switchgrass (PviGEA). The PviGEA contains quantitative transcript data for all major organ systems of switchgrass throughout development. We developed a web server that enables flexible, multifaceted analyses of PviGEA transcript data. The PviGEA was used to identify representatives of all known genes in the phenylpropanoid-monolignol biosynthesis pathway. © 2013 The Authors. The Plant Journal © 2013 Blackwell Publishing Ltd.The Plant Journal 01/2013; · 6.16 Impact Factor -
Article: Identification and characterization of petiolule-like pulvinus mutants with abolished nyctinastic leaf movement in the model legume Medicago truncatula.
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ABSTRACT: Leaves of many plant species open during the day and fold at night. Diurnal leaf movement, named nyctinasty, has been of great interest to researchers since Darwin's time. Nyctinastic leaf movement is generated by the pulvinus, which is a specialized motor organ located at the base of leaf and leaflet. The molecular basis and functional reason behind nyctinasty are unknown. In a forward screening of a retrotransposon-tagged mutant population of Medicago truncatula, four petiolule-like pulvinus (plp) mutant lines with defects in leaf movement were identified and characterized. Loss of function of PLP results in the change of pulvini to petiolules. PLP is specifically expressed in the pulvinus, as demonstrated by quantitative reverse-transcription polymerase chain reaction analysis, expression analysis of a PLP promoter-β-glucuronidase construct in transgenic plants and in situ hybridization. Microarray analysis revealed that the expression levels of many genes were altered in the mutant during the day and at night. Crosses between the plp mutant and several leaf pattern mutants showed that the developmental mechanisms of pulvini and leaf patterns are likely independent. Our results demonstrated that PLP plays a crucial role in the determination of pulvinus development. Leaf movement generated by pulvini may have an impact on plant vegetative growth.New Phytologist 08/2012; 196(1):92-100. · 6.64 Impact Factor -
Article: Collection and Analysis of Expressed Sequence Tags Derived from Laser Capture Microdissected Switchgrass (Panicum virgatum L. Alamo) Vascular Tissues
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ABSTRACT: Switchgrass is a perennial C4 grass that thrives in a wide range of North American habitats and is an emerging crop for the production of lignocellulosic biofuels. Lignin is an integral component of secondary plant cell walls that provides structural rigidity to the cell wall but it interferes with the conversion of cellulose to fermentable sugars by preventing chemical access to cellulose. Thus, one strategy for improving production of cellulosic ethanol is the down-regulation of lignin in plants. To achieve this goal, it is important to understand the molecular processes involved in vascular tissue development, lignification and secondary wall synthesis. Since active lignification occurs in the vascular system of the plant, we refined a protocol for isolating vascular tissues using laser-capture microdissection (LCM) in an effort to identify transcripts of switchgrass involved in lignification and secondary cell wall synthesis. ESTs (5,734) were sequenced from the cDNA libraries derived from laser microdissected vascular tissues. These Sanger sequences converged into 2,766 unigenes with an average length of 652bp. Gene ontology of the unigenes indicated that 11% of the sequences were lignin and cell wall related. Several transcription factors involved in lignin and secondary cell wall synthesis and sugar- or vesicle-mediated transporters were also present in this EST data set. In situ hybridization of seven representative genes confirmed the preferential expression of five genes in the vascular tissues. Comparison of our switchgrass vascular tissue derived ESTs with that of other plant species validated our LCM approach. Furthermore, our switchgrass vascular tissue ESTs revealed additional lignin and cell wall related genes that were not present in other existing switchgrass EST collections. Inventory of the switchgrass vascular tissue ESTs presented here provides an important genomic resource for mining genes to reduce recalcitrance in this important bioenergy crop. KeywordsExpressed sequence tags-Laser-capture microdissection-Lignin-Secondary cell wall-Switchgrass-Vascular tissueBioEnergy Research 04/2012; 3(3):278-294. · 3.56 Impact Factor -
Article: NO APICAL MERISTEM (MtNAM) regulates floral organ identity and lateral organ separation in Medicago truncatula.
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ABSTRACT: • The CUP-SHAPED COTYLEDON (CUC)/NO APICAL MERISTEM (NAM) family of genes control boundary formation and lateral organ separation, which is critical for proper leaf and flower patterning. However, most downstream targets of CUC/NAM genes remain unclear. • In a forward screen of the tobacco retrotransposon1 (Tnt1) insertion population in Medicago truncatula, we isolated a weak allele of the no-apical-meristem mutant mtnam-2. Meanwhile, we regenerated a mature plant from the null allele mtnam-1. These materials allowed us to extensively characterize the function of MtNAM and its downstream genes. • MtNAM is highly expressed in vegetative shoot buds and inflorescence apices, specifically at boundaries between the shoot apical meristem and leaf/flower primordia. Mature plants of the regenerated null allele and the weak allele display remarkable floral phenotypes: floral whorls and organ numbers are reduced and the floral organ identity is compromised. Microarray and quantitative RT-PCR analyses revealed that all classes of floral homeotic genes are down-regulated in mtnam mutants. Mutations in MtNAM also lead to fused cotyledons and leaflets of the compound leaf as well as a defective shoot apical meristem. • Our results revealed that MtNAM shares the role of CUC/NAM family genes in lateral organ separation and compound leaf development, and is also required for floral organ identity and development.New Phytologist 04/2012; 195(1):71-84. · 6.64 Impact Factor -
Article: Developmental Control of Lignification in Stems of Lowland Switchgrass Variety Alamo and the Effects on Saccharification Efficiency
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ABSTRACT: The switchgrass variety Alamo has been chosen for genome sequencing, genetic breeding, and genetic engineering by the US Department of Energy Joint Genome Institute (JGI) and the US Department of Energy BioEnergy Science Center. Lignin has been considered as a major obstacle for cellulosic biofuel production from switchgrass biomass. The purpose of this study was to provide baseline information on cell wall development in different parts of developing internodes of tillers of switchgrass cultivar Alamo and evaluate the effect of cell wall properties on biomass saccharification. Cell wall structure, soluble and wall-bound phenolics, and lignin content were analyzed from the top, middle, and bottom parts of internodes at different developmental stages using ultraviolet autofluorescence microscopy, histological staining methods, and high-performance liquid chromatography (HPLC). The examination of different parts of the developing internodes revealed differences in the stem structure during development, in the levels of free and well-bound phenolic compounds and lignin content, and in lignin pathway-related gene expression, indicating that the monolignol biosynthetic pathway in switchgrass is under complex spatial and temporal control. Our data clearly show that there was a strong negative correlation between overall lignin content and biomass saccharification efficiency. The ester-linked p-CA/FA ratio showed a positive correlation with lignin content and a negative correlation with sugar release. Our data provide baseline information to facilitate genetic modification of switchgrass recalcitrance traits for biofuel production.BioEnergy Research 04/2012; 2(4):233-245. · 3.56 Impact Factor -
Article: Several components of SKP1/Cullin/F-box E3 ubiquitin ligase complex and associated factors play a role in Agrobacterium-mediated plant transformation.
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ABSTRACT: • Successful genetic transformation of plants by Agrobacterium tumefaciens requires the import of bacterial T-DNA and virulence proteins into the plant cell that eventually form a complex (T-complex). The essential components of the T-complex include the single stranded T-DNA, bacterial virulence proteins (VirD2, VirE2, VirE3 and VirF) and associated host proteins that facilitate the transfer and integration of T-DNA. The removal of the proteins from the T-complex is likely achieved by targeted proteolysis mediated by VirF and the plant ubiquitin proteasome complex. • We evaluated the involvement of the host SKP1/culin/F-box (SCF)-E3 ligase complex and its role in plant transformation. Gene silencing, mutant screening and gene expression studies suggested that the Arabidopsis homologs of yeast SKP1 (suppressor of kinetochore protein 1) protein, ASK1 and ASK2, are required for Agrobacterium-mediated plant transformation. • We identified the role for SGT1b (suppressor of the G2 allele of SKP1), an accessory protein that associates with SCF-complex, in plant transformation. We also report the differential expression of many genes that encode F-box motif containing SKP1-interacting proteins (SKIP) upon Agrobacterium infection. • We speculate that these SKIP genes could encode the plant specific F-box proteins that target the T-complex associated proteins for polyubiquitination and subsequent degradation by the 26S proteasome.New Phytologist 04/2012; 195(1):203-16. · 6.64 Impact Factor -
Article: A novel HSI2 mutation in Arabidopsis affects the PHD-like domain and leads to derepression of seed-specific gene expression.
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ABSTRACT: Two related B3 domain transcriptional repressors, HSI2 (HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE2)/VAL1 (VP1/ABI3-LIKE1) and HSL1 (HSI2-LIKE1)/VAL2, function redundantly to repress key transcriptional regulators of seed maturation genes in Arabidopsis thaliana seedlings. Using a forward genetic screen designed to isolate trans-acting mutants that affected expression of a transgene containing the glutathione S-transferase F8 promoter::luciferase (GSTF8::LUC) reporter, we identified a novel HSI2 mutant allele, hsi2-4, that exhibits constitutively elevated luciferase expression while expression of the endogenous GSTF8 transcript remains unchanged. The hsi2-4 lesion was found to be a missense mutation that results in the substitution of a conserved cysteine within the plant homeodomain-like (PHD) motif of HSI2. Microarray analysis of hsi2-4 and hsi2-4 hsl1 mutants indicated that the HSI2 PHD-like domain functions non-redundantly to repress a subset of seed maturation genes, including those that encode AGL15 (AGAMOUS-LIKE15), FUSCA3 (FUS3), cruciferins, cupin family proteins, late-embryogenesis abundant protein, oleosins, 2S albumins and other seed-specific proteins in Arabidopsis seedlings. Many genes that are responsive to this mutation in the HSI2 PHD-like domain are enriched in histone H3 trimethylation on lysine 27 residues (H3K27me3), a repressive epigenetic mark. Chromatin immunoprecipitation analysis showed that sequences of the GSTF8::LUC transgene are enriched in H3K27me3 in a HSI2 PHD domain-dependent manner. These results indicate that the transcriptional repression activity of the HSI2 PHD domain could be mediated, at least in part, by its participation in the deposition of H3K27me3 on the chromatin of specific target genes.Planta 04/2012; 236(1):1-17. · 3.00 Impact Factor -
Article: Overexpression of miR156 in switchgrass (Panicum virgatum L.) results in various morphological alterations and leads to improved biomass production.
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ABSTRACT: Switchgrass (Panicum virgatum L.) has been developed into a dedicated herbaceous bioenergy crop. Biomass yield is a major target trait for genetic improvement of switchgrass. microRNAs have emerged as a prominent class of gene regulatory factors that has the potential to improve complex traits such as biomass yield. A miR156b precursor was overexpressed in switchgrass. The effects of miR156 overexpression on SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes were revealed by microarray and quantitative RT-PCR analyses. Morphological alterations, biomass yield, saccharification efficiency and forage digestibility of the transgenic plants were characterized. miR156 controls apical dominance and floral transition in switchgrass by suppressing its target SPL genes. Relatively low levels of miR156 overexpression were sufficient to increase biomass yield while producing plants with normal flowering time. Moderate levels of miR156 led to improved biomass but the plants were non-flowering. These two groups of plants produced 58%-101% more biomass yield compared with the control. However, high miR156 levels resulted in severely stunted growth. The degree of morphological alterations of the transgenic switchgrass depends on miR156 level. Compared with floral transition, a lower miR156 level is required to disrupt apical dominance. The improvement in biomass yield was mainly because of the increase in tiller number. Targeted overexpression of miR156 also improved solubilized sugar yield and forage digestibility, and offered an effective approach for transgene containment.Plant Biotechnology Journal 01/2012; 10(4):443-52. · 5.44 Impact Factor -
Article: Overexpression of AtLOV1 in Switchgrass Alters Plant Architecture, Lignin Content, and Flowering Time.
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ABSTRACT: Switchgrass (Panicum virgatum L.) is a prime candidate crop for biofuel feedstock production in the United States. As it is a self-incompatible polyploid perennial species, breeding elite and stable switchgrass cultivars with traditional breeding methods is very challenging. Translational genomics may contribute significantly to the genetic improvement of switchgrass, especially for the incorporation of elite traits that are absent in natural switchgrass populations. In this study, we constitutively expressed an Arabidopsis NAC transcriptional factor gene, LONG VEGETATIVE PHASE ONE (AtLOV1), in switchgrass. Overexpression of AtLOV1 in switchgrass caused the plants to have a smaller leaf angle by changing the morphology and organization of epidermal cells in the leaf collar region. Also, overexpression of AtLOV1 altered the lignin content and the monolignol composition of cell walls, and caused delayed flowering time. Global gene-expression analysis of the transgenic plants revealed an array of responding genes with predicted functions in plant development, cell wall biosynthesis, and flowering. To our knowledge, this is the first report of a single ectopically expressed transcription factor altering the leaf angle, cell wall composition, and flowering time of switchgrass, therefore demonstrating the potential advantage of translational genomics for the genetic improvement of this crop.PLoS ONE 01/2012; 7(12):e47399. · 4.09 Impact Factor -
Article: Overexpression of Fatty Acid Amide Hydrolase Induces Early Flowering in Arabidopsis thaliana.
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ABSTRACT: N-acylethanolamines (NAEs) are bioactive lipids derived from the hydrolysis of the membrane phospholipid N-acylphosphatidylethanolamine (NAPE). In animal systems this reaction is part of the "endocannabinoid" signaling pathway, which regulates a variety of physiological processes. The signaling function of NAE is terminated by fatty acid amide hydrolase (FAAH), which hydrolyzes NAE to ethanolamine and free fatty acid. Our previous work in Arabidopsis thaliana showed that overexpression of AtFAAH (At5g64440) lowered endogenous levels of NAEs in seeds, consistent with its role in NAE signal termination. Reduced NAE levels were accompanied by an accelerated growth phenotype, increased sensitivity to abscisic acid (ABA), enhanced susceptibility to bacterial pathogens, and early flowering. Here we investigated the nature of the early flowering phenotype of AtFAAH overexpression. AtFAAH overexpressors flowered several days earlier than wild type and AtFAAH knockouts under both non-inductive short day (SD) and inductive long day (LD) conditions. Microarray analysis revealed that the FLOWERING LOCUS T (FT) gene, which plays a major role in regulating flowering time, and one target MADS box transcription factor, SEPATALLA3 (SEP3), were elevated in AtFAAH overexpressors. Furthermore, AtFAAH overexpressors, with the early flowering phenotype had lower endogenous NAE levels in leaves compared to wild type prior to flowering. Exogenous application of NAE 12:0, which was reduced by up to 30% in AtFAAH overexpressors, delayed the onset of flowering in wild type plants. We conclude that the early flowering phenotype of AtFAAH overexpressors is, in part, explained by elevated FT gene expression resulting from the enhanced NAE hydrolase activity of AtFAAH, suggesting that NAE metabolism may participate in floral signaling pathways.Frontiers in plant science. 01/2012; 3:32. -
Article: Functional characterization of the switchgrass (Panicum virgatum) R2R3-MYB transcription factor PvMYB4 for improvement of lignocellulosic feedstocks.
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ABSTRACT: • The major obstacle for bioenergy production from switchgrass biomass is the low saccharification efficiency caused by cell wall recalcitrance. Saccharification efficiency is negatively correlated with both lignin content and cell wall ester-linked p-coumarate: ferulate (p-CA : FA) ratio. In this study, we cloned and functionally characterized an R2R3-MYB transcription factor from switchgrass and evaluated its potential for developing lignocellulosic feedstocks. • The switchgrass PvMYB4 cDNAs were cloned and expressed in Escherichia coli, yeast, tobacco and switchgrass for functional characterization. Analyses included determination of phylogenetic relations, in situ hybridization, electrophoretic mobility shift assays to determine binding sites in target promoters, and protoplast transactivation assays to demonstrate domains active on target promoters. • PvMYB4 binds to the AC-I, AC-II and AC-III elements of monolignol pathway genes and down-regulates these genes in vivo. Ectopic overexpression of PvMYB4 in transgenic switchgrass resulted in reduced lignin content and ester-linked p-CA : FA ratio, reduced plant stature, increased tillering and an approx. threefold increase in sugar release efficiency from cell wall residues. • We describe an alternative strategy for reducing recalcitrance in switchgrass by manipulating the expression of a key transcription factor instead of a lignin biosynthetic gene. PvMYB4-OX transgenic switchgrass lines can be used as potential germplasm for improvement of lignocellulosic feedstocks and provide a platform for further understanding gene regulatory networks underlying switchgrass cell wall recalcitrance.New Phytologist 01/2012; 193(1):121-36. · 6.64 Impact Factor -
Article: Loss of abaxial leaf epicuticular wax in Medicago truncatula irg1/palm1 mutants results in reduced spore differentiation of anthracnose and nonhost rust pathogens.
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ABSTRACT: To identify genes that confer nonhost resistance to biotrophic fungal pathogens, we did a forward-genetics screen using Medicago truncatula Tnt1 retrotransposon insertion lines. From this screen, we identified an inhibitor of rust germ tube differentation1 (irg1) mutant that failed to promote preinfection structure differentiation of two rust pathogens, Phakopsora pachyrhizi and Puccinia emaculata, and one anthracnose pathogen, Colletotrichum trifolii, on the abaxial leaf surface. Cytological and chemical analyses revealed that the inhibition of rust preinfection structures in irg1 mutants is due to complete loss of the abaxial epicuticular wax crystals and reduced surface hydrophobicity. The composition of waxes on abaxial leaf surface of irg1 mutants had >90% reduction of C30 primary alcohols and a preferential increase of C29 and C31 alkanes compared with the wild type. IRG1 encodes a Cys(2)His(2) zinc finger transcription factor, PALM1, which also controls dissected leaf morphology in M. truncatula. Transcriptome analysis of irg1/palm1 mutants revealed downregulation of eceriferum4, an enzyme implicated in primary alcohol biosynthesis, and MYB96, a major transcription factor that regulates wax biosynthesis. Our results demonstrate that PALM1 plays a role in regulating epicuticular wax metabolism and transport and that epicuticular wax influences spore differentiation of host and nonhost fungal pathogens.The Plant Cell 01/2012; 24(1):353-70. · 8.99 Impact Factor -
Article: From model to crop: functional analysis of a STAY-GREEN gene in the model legume Medicago truncatula and effective use of the gene for alfalfa improvement.
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ABSTRACT: Medicago truncatula has been developed into a model legume. Its close relative alfalfa (Medicago sativa) is the most widely grown forage legume crop in the United States. By screening a large population of M. truncatula mutants tagged with the transposable element of tobacco (Nicotiana tabacum) cell type1 (Tnt1), we identified a mutant line (NF2089) that maintained green leaves and showed green anthers, central carpels, mature pods, and seeds during senescence. Genetic and molecular analyses revealed that the mutation was caused by Tnt1 insertion in a STAY-GREEN (MtSGR) gene. Transcript profiling analysis of the mutant showed that loss of the MtSGR function affected the expression of a large number of genes involved in different biological processes. Further analyses revealed that SGR is implicated in nodule development and senescence. MtSGR expression was detected across all nodule developmental zones and was higher in the senescence zone. The number of young nodules on the mutant roots was higher than in the wild type. Expression levels of several nodule senescence markers were reduced in the sgr mutant. Based on the MtSGR sequence, an alfalfa SGR gene (MsSGR) was cloned, and transgenic alfalfa lines were produced by RNA interference. Silencing of MsSGR led to the production of stay-green transgenic alfalfa. This beneficial trait offers the opportunity to produce premium alfalfa hay with a more greenish appearance. In addition, most of the transgenic alfalfa lines retained more than 50% of chlorophylls during senescence and had increased crude protein content. This study illustrates the effective use of knowledge gained from a model system for the genetic improvement of an important commercial crop.Plant physiology 09/2011; 157(3):1483-96. · 6.53 Impact Factor -
Article: System responses to long-term drought and re-watering of two contrasting alfalfa varieties.
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ABSTRACT: Systems analysis of two alfalfa varieties, Wisfal (Medicago sativa ssp. falcata var. Wisfal) and Chilean (M. sativa ssp. sativa var. Chilean), with contrasting tolerance/sensitivity to drought revealed common and divergent responses to drought stress. At a qualitative level, molecular, biochemical, and physiological responses to drought stress were similar in the two varieties, indicating that they employ the same strategies to cope with drought. However, quantitative differences in responses at all levels were revealed that may contribute to greater drought tolerance in Wisfal. These included lower stomatal density and conductance in Wisfal; delayed leaf senescence compared with Chilean; greater root growth following a drought episode, and greater accumulation of osmolytes, including raffinose and galactinol, and flavonoid antioxidants in roots and/or shoots of Wisfal. Genes encoding transcription factors and other regulatory proteins, and genes involved in the biosynthesis of osmolytes and (iso)flavonoids were differentially regulated between the two varieties and represent potential targets for improving drought tolerance in alfalfa in the future.The Plant Journal 08/2011; 68(5):871-89. · 6.16 Impact Factor -
Article: STENOFOLIA regulates blade outgrowth and leaf vascular patterning in Medicago truncatula and Nicotiana sylvestris.
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ABSTRACT: Dicot leaf primordia initiate at the flanks of the shoot apical meristem and extend laterally by cell division and cell expansion to form the flat lamina, but the molecular mechanism of lamina outgrowth remains unclear. Here, we report the identification of STENOFOLIA (STF), a WUSCHEL-like homeobox transcriptional regulator, in Medicago truncatula, which is required for blade outgrowth and leaf vascular patterning. STF belongs to the MAEWEST clade and its inactivation by the transposable element of Nicotiana tabacum cell type1 (Tnt1) retrotransposon insertion leads to abortion of blade expansion in the mediolateral axis and disruption of vein patterning. We also show that the classical lam1 mutant of Nicotiana sylvestris, which is blocked in lamina formation and stem elongation, is caused by deletion of the STF ortholog. STF is expressed at the adaxial-abaxial boundary layer of leaf primordia and governs organization and outgrowth of lamina, conferring morphogenetic competence. STF does not affect formation of lateral leaflets but is critical to their ability to generate a leaf blade. Our data suggest that STF functions by modulating phytohormone homeostasis and crosstalk directly linked to sugar metabolism, highlighting the importance of coordinating metabolic and developmental signals for leaf elaboration.The Plant Cell 06/2011; 23(6):2125-42. · 8.99 Impact Factor -
Article: The plastidial folylpolyglutamate synthetase and root apical meristem maintenance.
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ABSTRACT: Folylpolyglutamate synthetase (FPGS) catalyzes the attachment of glutamate residues to the folate molecule in plants. Three isoforms of FPGS have been identified in Arabidopsis and these are localized in the plastid (AtDFB), mitochondria (AtDFC), and cytosol (AtDFD). We recently determined that mutants in the AtDFB (At5G05980) gene disrupt primary root development in Arabidopsis thaliana seedlings. Transient expression of AtDFB-green fluorescent protein (GFP) fusion under the control of the native AtDFB promoter in Nicotiana tabacum leaf epidermal cells verified the plastid localization of AtDFB. Furthermore, low concentrations of methotrexate (MTX), a compound commonly used as a folate antagonist in plant and mammalian cells induced primary root defects in wild type seedlings that were similar to atdfb. In addition, atdfb seedlings were more sensitive to MTX when compared to wild type. Quantitative (q) RT-PCR showed lower transcript levels of the mitochondrial and cytosolic FPGS in roots of 7 day old atdfb seedling suggesting feedback regulation of AtDFB on the expression of other FPGS isoforms during early seedling development. The primary root defects of atdfb, which can be traced in part to altered quiescent center (QC) identity, pave the way for future studies that could link cell type specific folate and FPGS isoform requirements to whole organ development.Plant signaling & behavior 05/2011; 6(5):751-4. -
Article: MATE2 mediates vacuolar sequestration of flavonoid glycosides and glycoside malonates in Medicago truncatula.
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ABSTRACT: The majority of flavonoids, such as anthocyanins, proanthocyanidins, and isoflavones, are stored in the central vacuole, but the molecular basis of flavonoid transport is still poorly understood. Here, we report the functional characterization of a multidrug and toxin extrusion transporter (MATE2), from Medicago truncatula. MATE 2 is expressed primarily in leaves and flowers. Despite its high similarity to the epicatechin 3'-O-glucoside transporter MATE1, MATE2 cannot efficiently transport proanthocyanidin precursors. In contrast, MATE2 shows higher transport capacity for anthocyanins and lower efficiency for other flavonoid glycosides. Three malonyltransferases that are coexpressed with MATE2 were identified. The malonylated flavonoid glucosides generated by these malonyltransferases are more efficiently taken up into MATE2-containing membrane vesicles than are the parent glycosides. Malonylation increases both the affinity and transport efficiency of flavonoid glucosides for uptake by MATE2. Genetic loss of MATE2 function leads to the disappearance of leaf anthocyanin pigmentation and pale flower color as a result of drastic decreases in the levels of various flavonoids. However, some flavonoid glycoside malonates accumulate to higher levels in MATE2 knockouts than in wild-type controls. Deletion of MATE2 increases seed proanthocyanidin biosynthesis, presumably via redirection of metabolic flux from anthocyanin storage.The Plant Cell 04/2011; 23(4):1536-55. · 8.99 Impact Factor
Top co-authors
Top Journals
- The Plant Journal (6)
- New Phytologist (6)
- Plant physiology (5)
- The Plant Cell (4)
- Planta (3)
Institutions
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2006–2013
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The Samuel Roberts Noble Foundation
- Division of Plant Biology
Ardmore, OK, USA
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2012
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U.S. Department of Energy
Washington, D. C., DC, USA
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2009
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West Virginia University
- Division of Plant and Soil Sciences
Morgantown, WV, USA
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