[Show abstract][Hide abstract] ABSTRACT: Ethylene and abscisic acid (ABA) act synergistically or antagonistically to regulate plant growth and development. ABA is derived from the carotenoid biosynthesis pathway. Here, we analyzed the interplay among ethylene, carotenoid biogenesis, and ABA in rice (Oryza sativa) using the rice ethylene response mutant mhz5, which displays a reduced ethylene response in roots but an enhanced ethylene response in coleoptiles. We found that MHZ5 encodes a carotenoid isomerase and that the mutation in mhz5 blocks carotenoid biosynthesis, reduces ABAaccumulation, and promotes ethylene production in etiolated seedlings. ABA can largely rescue the ethylene response of the mhz5 mutant. Ethylene induces MHZ5expression, the production of neoxanthin, an ABA biosynthesis precursor, andABA accumulation in roots. MHZ5 overexpression results in enhanced ethylene sensitivity in roots and reduced ethylene sensitivity in coleoptiles. Mutation or overexpression of MHZ5 also alters the expression of ethylene-responsive genes. Genetic studies revealed that the MHZ5-mediated ABA pathway acts downstream of ethylene signaling to inhibit root growth. The MHZ5-mediated ABA pathway likely acts upstream but negatively regulates ethylene signaling to control coleoptile growth. Our study reveals novel interactions among ethylene, carotenogenesis, and ABA and provides insight into improvements in agronomic traits and adaptive growth through the manipulation of these pathways in rice.
The Plant Cell 04/2015; 27(4). DOI:10.1105/tpc.15.00080 · 9.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The orange head phenotype of Br - or resulted from a large insertion in carotenoid isomerase (BrCRTISO) . Comparative transcriptome analysis revealed that the mutation affected the expression of abundant transcription factor genes. A new orange trait-specific marker was developed for marker-assisted breeding. Orange head leaves are a desirable quality trait for Chinese cabbage. Our previous fine mapping identified BrCRTISO as the Br-or candidate gene for the orange Chinese cabbage mutant. Here, we examined the BrCRTISO gene from white and orange head Chinese cabbage. While BrCRTISO from the white control plant was able to complement the Arabidopsis Atcrtiso mutant phenotype, Brcrtiso with a large insertion from the orange head Chinese cabbage failed to rescue the Arabidopsis mutant phenotype. The results show that Brcrtiso was non-functional, concomitant with the accumulation of prolycopene in Br-or to yield orange head. Comparative transcriptome analysis by RNA-seq identified 372 differentially expressed genes between the control and Br-or mutant using two near-isogenic lines with white and orange inner leaves. The mutation in BrCRTISO specifically affected many genes in the functional groups involved in RNA, protein, transport, and signaling. Particularly, expressions of many transcription factor genes were dramatically altered in Br-or, suggesting a potential role of BrCRTISO or carotenoid metabolites in affecting transcription. A novel co-dominant gene-specific marker was developed that co-segregated with orange color phenotype and would be useful for marker-assisted selection with enhanced selection efficiency. Our study provides new insights into understanding of the molecular basis of Br-or in mediating head leaf color and depicts a global view of the effect of BrCRTISO on cellular processes in plant. It also provides a molecular tool to accelerate breeding new Chinese cabbage cultivars with unique health quality and visual appearance.
[Show abstract][Hide abstract] ABSTRACT: Thigmomorphogenesis is viewed as being a response process of acclimation to short repetitive bursts of mechanical stimulation or touch. The underlying molecular mechanisms that coordinate changes in how touch signals lead to long-term morphological changes are enigmatic. Touch responsive gene expression is rapid and transient, and no transcription factor or DNA regulatory motif has been reported that could confer a genome wide mechanical stimulus. We report here on a chromatin modifying enzyme, SDG8/ASHH2, which can regulate the expression of many touch responsive genes identified in Arabidopsis. SDG8 is required for the permissive expression of touch induced genes; and the loss of function of sdg8 perturbs the maximum levels of induction on selected touch gene targets. SDG8 is required to maintain permissive H3K4 trimethylation marks surrounding the Arabidopsis touch-inducible gene TOUCH 3 (TCH3), which encodes a calmodulin-like protein (CML12). The gene neighboring was also slightly down regulated, revealing a new target for SDG8 mediated chromatin modification. Finally, sdg8 mutants show perturbed morphological response to wind-agitated mechanical stimuli, implicating an epigenetic memory-forming process in the acclimation response of thigmomorphogenesis.
[Show abstract][Hide abstract] ABSTRACT: In addition to acting as photoprotective compounds, carotenoids also serve as precursors in the biosynthesis of several phytohormones and proposed regulatory signals. Here, we report a signaling process derived from carotenoids that regulates early chloroplast and leaf development. Biosynthesis of the signal depends on ζ-carotene desaturase activity encoded by the ζ-CAROTENE DESATURASE (ZDS)/CHLOROPLAST BIOGENESIS5 (CLB5) gene in Arabidopsis thaliana. Unlike other carotenoid-deficient plants, zds/clb5 mutant alleles display profound alterations in leaf morphology and cellular differentiation as well as altered expression of many plastid- and nucleus-encoded genes. The leaf developmental phenotypes and gene expression alterations of zds/clb5/spc1/pde181 plants are rescued by inhibitors or mutations of phytoene desaturase, demonstrating that phytofluene and/or ζ-carotene are substrates for an unidentified signaling molecule. Our work further demonstrates that this signal is an apocarotenoid whose synthesis requires the activity of the carotenoid cleavage dioxygenase CCD4.
The Plant Cell 06/2014; 26(6). DOI:10.1105/tpc.114.123349 · 9.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In plants, continuous formation of lateral roots (LRs) facilitates efficient exploration of the soil environment. Roots can maximize developmental capacity in variable environmental conditions through establishment of sites competent to form LRs. This LR prepattern is established by a periodic oscillation in gene expression near the root tip. The spatial distribution of competent (prebranch) sites results from the interplay between this periodic process and primary root growth; yet, much about this oscillatory process and the formation of prebranch sites remains unknown. We find that disruption of carotenoid biosynthesis results in seedlings with very few LRs. Carotenoids are further required for the output of the LR clock because inhibition of carotenoid synthesis also results in fewer sites competent to form LRs. Genetic analyses and a carotenoid cleavage inhibitor indicate that an apocarotenoid, distinct from abscisic acid or strigolactone, is specifically required for LR formation. Expression of a key carotenoid biosynthesis gene occurs in a spatially specific pattern along the root's axis, suggesting spatial regulation of carotenoid synthesis. These results indicate that developmental prepatterning of LRs requires an uncharacterized carotenoid-derived molecule. We propose that this molecule functions non-cell-autonomously in establishment of the LR prepattern.
Proceedings of the National Academy of Sciences 03/2014; 111(13). DOI:10.1073/pnas.1403016111 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Agriculture requires a second green revolution to provide increased food, fodder, fiber, fuel and soil fertility for a growing population while being more resilient to extreme weather on finite land, water, and nutrient resources. Advances in phenomics, genomics and environmental control/sensing can now be used to directly select yield and resilience traits from large collections of germplasm if software can integrate among
the technologies. Traits could be Captured throughout development and across environments from multi-dimensional phenotypes, by applying Genome Wide Association Studies (GWAS) to identify causal genes and background variation and functional structural plant models (FSPMs) to predict plant growth and reproduction in target environments. TraitCapture should be applicable to both controlled and field environments and would allow breeders to simulate regional variety trials to pre-select for increased productivity under challenging environments.
Current Opinion in Plant Biology 03/2014; 18:73-79. DOI:10.1016/j.pbi.2014.02.002 · 9.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cellular auxin homeostasis controls many aspects of plant growth, organogenesis and development. The existence of intracellular auxin transport mediated by endoplasmic reticulum (ER)-localized PIN5, PIN6 and PIN8 proteins is a relatively recent discovery shaping a new era in understanding auxin-mediated growth processes. Here we summarize the importance of PIN6 in mediating intracellular auxin transport during root formation, leaf vein patterning and nectary production. While, it was previously shown that PIN6 was strongly expressed in rosette leaf cell types important in vein formation, here we demonstrate by use a PIN6 promoter-reporter fusion, that PIN6 is also preferentially expressed in the vasculature of the primary root, cotyledons, cauline leaves, floral stem, sepals and the main transmitting tract of the reproductive silique. The strong, vein- specific reporter gene expression patterns enabled by the PIN6 promoter emphasizes that transcriptional control is likely to be a major regulator of PIN6 protein levels, during vasculature formation, and supports the need for ER-localized PIN proteins in selecting specialized cells for vascular function in land plants.
[Show abstract][Hide abstract] ABSTRACT: The cytosol is the fluid portion of the cell that is not partitioned by membranes. It contains a highly diverse collection of substances and is central to many essential cellular processes ranging from signal transduction, metabolite production and transport, protein biosynthesis and degradation to stress response and defense. Despite its importance, only a few proteomic studies have been performed on the plant cytosol. This is largely due to difficulties in isolating relatively pure samples from plant material free of disrupted organelle material. In this chapter we outline methods for isolating the cytosolic fraction from Arabidopsis cell cultures and seedlings and provide guidance on assessing purity for analysis by mass spectrometry.
[Show abstract][Hide abstract] ABSTRACT: Excess light can have a negative impact on photosynthesis, thus plants have evolved many different ways to adapt to different light conditions to both optimize energy use and avoid damage caused by excess light. Analysis of the snowy cotyledon 4 (sco4) mutant revealed a mutation in a chloroplast-targeted protein which shares limited homology with CaaX-type-endopeptidases. The SCO4 protein possesses an important function in photosynthesis and development, with point mutations rendering the seedlings and adult plants susceptible to photo-oxidative stress. The sco4 mutation impairs acclimation of chloroplasts and their photosystems to excess light, evidenced in a reduction in PS I function, decreased linear electron transfer, yet increased non-photochemical quenching. SCO4 is localized to the chloroplasts and suggests the existence of an unreported type of protein modification within this organelle. Phylogenetic and yeast complementation analyses of SCO4-like proteins reveals that SCO4 is a member of a unknown group of higher plant-specific proteinases quite distinct from the well described CaaX-type endopeptidases RCE1 and STE24 and lacks canonical CaaX activity. Therefore, we hypothesize that SCO4 is a novel endopeptidase required for critical protein modifications within chloroplasts, influencing the function of proteins involved in photosynthesis required for tolerance to excess light.
[Show abstract][Hide abstract] ABSTRACT: Background / Purpose:
Plants have a range of photo-protective mechanisms to prevent damage. Looking for variations in natural populations may identify novel genes and alleles responsible for photoprotection.
Our preliminary results show that high throughput fluorescence imaging methods using TrayScan can be used to study photoprotective mechanisms in large populations. Using this method and analysis pipeline for QTL mapping we can identify novel genes which relate to non-photochemical quenching (NPQ).
24th International Conference on Arabidopsis Research (ICAR) 2013; 08/2013
[Show abstract][Hide abstract] ABSTRACT: Sunlight provides energy for photosynthesis and is essential for nearly all life on earth. However, too much or too little light or rapidly fluctuating light conditions cause stress to plants. Rapid changes in the amount of light are perceived as a change in the reduced/oxidized (redox) state of photosynthetic electron transport components in chloroplasts. However, how this generates a signal that is relayed to changes in nuclear gene expression is not well understood. We modified redox state in the reference plant, Arabidopsis thaliana, using either excess light or low light plus the herbicide DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone), a well-known inhibitor of photosynthetic electron transport. Modification of redox state caused a change in expression of a common set of about 750 genes, many of which are known stress-responsive genes. Among the most highly enriched promoter elements in the induced gene set were heat-shock elements (HSEs), known motifs that change gene expression in response to high temperature in many systems. We show that HSEs from the promoter of the ASCORBATE PEROXIDASE 2 (APX2) gene were necessary and sufficient for APX2 expression in conditions of excess light, or under low light plus the herbicide. We tested APX2 expression phenotypes in overexpression and loss-of-function mutants of 15 Arabidopsis A-type heat-shock transcription factors (HSFs), and identified HSFA1D, HSFA2, and HSFA3 as key factors regulating APX2 expression in diverse stress conditions. Excess light regulates both the subcellular location of HSFA1D and its biochemical properties, making it a key early component of the excess light stress network of plants.
Proceedings of the National Academy of Sciences 08/2013; 110(35). DOI:10.1073/pnas.1311632110 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin-regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development.
PLoS ONE 07/2013; 8(7):e70069. DOI:10.1371/journal.pone.0070069 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Systemic signalling of photooxidative stress from a high light (HL)-exposed leaf to a shaded leaf results in systemic acquired acclimation (SAA) in the distal tissue. As yet unanswered questions in systemic photooxidative stress signalling are in regard to what type of signal and what form of travel the signal takes from a small area of exposed tissue to as yet unstressed distal tissues. Issues such as the specificity of different stress responses, how different ROS signalling pathways converge, and antagonistically regulated systems are all currently being investigated. The majority of studies in this field, however, focus on the intercellular signalling aspects rather than leaf-to-leaf movement of the signal. Traditional studies of biotic long-distance signalling have not as yet been comprehensively applied to abiotic stress signalling research, particularly in regard to whether an abiotic signal is able to rapidly travel through the vasculature from leaf to leaf. This review covers literature relating to the effects that HL intensity and the production of ROS have on the stress signalling processes of light perception, retrograde and intercellular signalling, as well as leaf-to-leaf systemic signalling in the model organism Arabidopsis thaliana.
Long-Distance Systemic Signaling and Communication in Plants, Edited by František Baluška, 01/2013: chapter Systemic Photooxidative Stress Signalling: pages 251-274; Springer Berlin Heidelberg., ISBN: 978-3-642-36470-9
[Show abstract][Hide abstract] ABSTRACT: Background
Plant grafting techniques have deepened our understanding of the signals facilitating communication between the root and shoot, as well as between shoot and reproductive organs. Transmissible signalling molecules can include hormones, peptides, proteins and metabolites: some of which travel long distances to communicate stress, nutrient status, disease and developmental events. While hypocotyl micrografting techniques have been successfully established for Arabidopsis to explore root to shoot communications, inflorescence grafting in Arabidopsis has not been exploited to the same extent. Two different strategies (horizontal and wedge-style inflorescence grafting) have been developed to explore long distance signalling between the shoot and reproductive organs. We developed a robust wedge-cleft grafting method, with success rates greater than 87%, by developing better tissue contact between the stems from the inflorescence scion and rootstock. We describe how to perform a successful inflorescence stem graft that allows for reproducible translocation experiments into the physiological, developmental and molecular aspects of long distance signalling events that promote reproduction.
Wedge grafts of the Arabidopsis inflorescence stem were supported with silicone tubing and further sealed with parafilm to maintain the vascular flow of nutrients to the shoot and reproductive tissues. Nearly all (87%) grafted plants formed a strong union between the scion and rootstock. The success of grafting was scored using an inflorescence growth assay based upon the growth of primary stem. Repeated pruning produced new cauline tissues, healthy flowers and reproductive siliques, which indicates a healthy flow of nutrients from the rootstock. Removal of the silicone tubing showed a tightly fused wedge graft junction with callus proliferation. Histological staining of sections through the graft junction demonstrated the differentiation of newly formed vascular connections, parenchyma tissue and lignin accumulation, supporting the presumed success of the graft union between two sections of the primary inflorescence stem.
We describe a simple and reliable method for grafting sections of an Arabidopsis inflorescence stem. This step-by-step protocol facilitates laboratories without grafting experience to further explore the molecular and chemical signalling which coordinates communications between the shoot and reproductive tissues.
[Show abstract][Hide abstract] ABSTRACT: Half a century of research into the physiology and biochemistry of sun-shade acclimation in diverse plants has provided reality checks for contemporary understanding of thylakoid membrane dynamics. This paper reviews recent insights into photosynthetic efficiency and photoprotection from studies of two xanthophyll cycles in old shade leaves from the inner canopy of the tropical trees Inga sapindoides and Persea americana (avocado). It then presents new physiological data from avocado on the time frames of the slow coordinated photosynthetic development of sink leaves in sunlight and on the slow renovation of photosynthetic properties in old leaves during sun to shade and shade to sun acclimation. In so doing, it grapples with issues in vivo that seem relevant to our increasingly sophisticated understanding of ΔpH-dependent, xanthophyll-pigment-stabilized non-photochemical quenching in the antenna of PSII in thylakoid membranes in vitro.
Philosophical Transactions of The Royal Society B Biological Sciences 12/2012; 367(1608):3503-14. DOI:10.1098/rstb.2012.0072 · 6.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study resolved correlations between changes in xanthophyll pigments and photosynthetic properties in attached and detached shade-grown avocado leaves upon sun exposure. Lutein epoxide (Lx) was de-epoxidized to lutein (ΔL) over 5 h, whereas violaxanthin (V) conversion to antheraxanthin (A) and zeaxanthin (Z) ceased after 1 h. During subsequent dark or shade recovery, de novo synthesis of L and Z continued, followed by epoxidation of A and Z, but not of L. Light saturated non-photochemical quenching (NPQ) was strongly and linearly correlated with decreasing [Lx] and increasing [L] but showed a biphasic correlation with declining [V] and increasing [A+Z] separated when V de-epoxidation ceased. When considering [ΔL+Z], the monophasic linear correlation was restored. Photochemical efficiency of PSII (Fv/Fm) and PSII/PSI (deduced from delivery of electrons to PSI in saturating single turnover flashes) showed a strong correlation in their continuous decline in sunlight and the increase in NPQ capacity. This decrease was also reflected in the initial reduction of the slope of photosynthetic electron transport (ETR) vs. PFD. Generally longer, stronger sun exposures enhanced declines in both slope and maximum ETR rates as well as Fv/Fm and PSII/PSI more severely and prevented full recovery. Interestingly, increased NPQ capacity was accompanied by slower relaxation. This was more prominent in detached leaves with closed stomata, indicating photorespiratory recycling of CO2 provided little photoprotection to avocado shade leaves. Sun exposure of these shade leaves initiates a continuum of photoprotection, beyond full engagement of Lx-and V-cycle in the antenna, but ultimately photoinactivated PSII reaction centers.