[Show abstract][Hide abstract] ABSTRACT: CRK5 is a member of the Arabidopsis thaliana Ca(2+)/calmodulin-dependent kinase-related kinase family. Here, we show that inactivation of CRK5 inhibits primary root elongation and delays gravitropic bending of shoots and roots. Reduced activity of the auxin-induced DR5-green fluorescent protein reporter suggests that auxin is depleted from crk5 root tips. However, no tip collapse is observed and the transcription of genes for auxin biosynthesis, AUXIN TRANSPORTER/AUXIN TRANSPORTER-LIKE PROTEIN (AUX/LAX) auxin influx, and PIN-FORMED (PIN) efflux carriers is unaffected by the crk5 mutation. Whereas AUX1, PIN1, PIN3, PIN4, and PIN7 display normal localization, PIN2 is depleted from apical membranes of epidermal cells and shows basal to apical relocalization in the cortex of the crk5 root transition zone. This, together with an increase in the number of crk5 lateral root primordia, suggests facilitated auxin efflux through the cortex toward the elongation zone. CRK5 is a plasma membrane-associated kinase that forms U-shaped patterns facing outer lateral walls of epidermis and cortex cells. Brefeldin inhibition of exocytosis stimulates CRK5 internalization into brefeldin bodies. CRK5 phosphorylates the hydrophilic loop of PIN2 in vitro, and PIN2 shows accelerated accumulation in brefeldin bodies in the crk5 mutant. Delayed gravitropic response of the crk5 mutant thus likely reflects defective phosphorylation of PIN2 and deceleration of its brefeldin-sensitive membrane recycling.
The Plant Cell 05/2013; 25(5). DOI:10.1105/tpc.113.110452 · 9.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Active polar transport establishes directional auxin flow and the generation of local auxin gradients implicated in plant responses and development. Auxin modulates gravitropism at the root tip and root hair morphogenesis at the differentiation zone. Genetic and biochemical analyses provide evidence for defective basipetal auxin transport in trh1 roots. The trh1, pin2, axr2 and aux1 mutants, and transgenic plants overexpressing PIN1, all showing impaired gravity response and root hair development, revealed ectopic PIN1 localization. The auxin antagonist hypaphorine blocked root hair elongation and caused moderate agravitropic root growth, also leading to PIN1 mislocalization. These results suggest that auxin imbalance leads to proximal and distal developmental defects in Arabidopsis root apex, associated with agravitropic root growth and root hair phenotype, respectively, providing evidence that these two auxin-regulated processes are coupled. Cell-specific subcellular localization of TRH1-YFP in stele and epidermis supports TRH1 engagement in auxin transport, and hence impaired function in trh1 causes dual defects of auxin imbalance. The interplay between intrinsic cues determining root epidermal cell fate through the TTG/GL2 pathway and environmental cues including abiotic stresses modulates root hair morphogenesis. As a consequence of auxin imbalance in Arabidopsis root apex, ectopic PIN1 mislocalization could be a risk aversion mechanism to trigger root developmental responses ensuring root growth plasticity.
New Phytologist 12/2012; 197(4). DOI:10.1111/nph.12092 · 7.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plant roots show an impressive degree of plasticity in adapting their branching patterns to ever-changing growth conditions. An important mechanism underlying this adaptation ability is the interaction between hormonal and developmental signals. Here, we analyze the interaction of jasmonate with auxin to regulate lateral root (LR) formation through characterization of an Arabidopsis thaliana mutant, jasmonate-induced defective lateral root1 (jdl1/asa1-1). We demonstrate that, whereas exogenous jasmonate promotes LR formation in wild-type plants, it represses LR formation in jdl1/asa1-1. JDL1 encodes the auxin biosynthetic gene ANTHRANILATE SYNTHASE alpha1 (ASA1), which is required for jasmonate-induced auxin biosynthesis. Jasmonate elevates local auxin accumulation in the basal meristem of wild-type roots but reduces local auxin accumulation in the basal meristem of mutant roots, suggesting that, in addition to activating ASA1-dependent auxin biosynthesis, jasmonate also affects auxin transport. Indeed, jasmonate modifies the expression of auxin transport genes in an ASA1-dependent manner. We further provide evidence showing that the action mechanism of jasmonate to regulate LR formation through ASA1 differs from that of ethylene. Our results highlight the importance of ASA1 in jasmonate-induced auxin biosynthesis and reveal a role for jasmonate in the attenuation of auxin transport in the root and the fine-tuning of local auxin distribution in the root basal meristem.
The Plant Cell 06/2009; 21(5):1495-511. DOI:10.1105/tpc.108.064303 · 9.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Transformation of plant cells with T-DNA of virulent agrobacteria is one of the most extreme triggers of developmental changes in higher plants. For rapid growth and development of resulting tumors, specific changes in the gene expression profile and metabolic adaptations are required. Increased transport and metabolic fluxes are critical preconditions for growth and tumor development. A functional genomics approach, using the Affymetrix whole genome microarray (approximately 22,800 genes), was applied to measure changes in gene expression. The solute pattern of Arabidopsis thaliana tumors and uninfected plant tissues was compared with the respective gene expression profile. Increased levels of anions, sugars, and amino acids were correlated with changes in the gene expression of specific enzymes and solute transporters. The expression profile of genes pivotal for energy metabolism, such as those involved in photosynthesis, mitochondrial electron transport, and fermentation, suggested that tumors produce C and N compounds heterotrophically and gain energy mainly anaerobically. Thus, understanding of gene-to-metabolite networks in plant tumors promotes the identification of mechanisms that control tumor development.
The Plant Cell 01/2007; 18(12):3617-34. DOI:10.1105/tpc.106.044743 · 9.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Apical hook establishment and maintenance is an important developmental process driven by multiple hormonal cross talk. The
importance of ethylene and asymmetric auxin-distribution, the requirement of gibberellins and the role of brassinosteroids
have been demonstrated previously (Bleecker et al. 1988; Lehman et al. 1996; Chory et al. 1991; Achard et al. 2003; Vriezen et al. 2004). In the light, a similar complexity of hormonal regulation has been revealed wherein all aforementioned hormones can
stimulate hypocotyl elongation.
[Show abstract][Hide abstract] ABSTRACT: In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry, and lateral growth. In trn mutants, the leaf venation network had a severely reduced complexity: incomplete loops, no tertiary or quaternary veins, and vascular islands. The leaf laminas were asymmetric and narrow because of a severely reduced cell number. We postulate that the imbalance between cell proliferation and cell differentiation and the altered auxin distribution in both trn mutants cause asymmetric leaf growth and aberrant venation patterning. TRN1 and TRN2 were epistatic to ASYMMETRIC LEAVES1 with respect to leaf asymmetry, consistent with their expression in the shoot apical meristem and leaf primordia. TRN1 codes for a large plant-specific protein with conserved domains also found in a variety of signaling proteins, whereas TRN2 encodes a transmembrane protein of the tetraspanin family whose phylogenetic tree is presented. Double mutant analysis showed that TRN1 and TRN2 act in the same pathway.
The Plant Cell 05/2006; 18(4):852-66. DOI:10.1105/tpc.105.040568 · 9.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dark-grown Arabidopsis seedlings develop an apical hook by differential cell elongation and division, a process driven by cross-talk between multiple hormones. Auxins, ethylene and gibberellins interact in the formation of the apical hook. In the light, a similar complexity of hormonal regulation has been revealed at the level of hypocotyl elongation. Here, we describe the involvement of brassinosteroids (BRs) in auxin- and ethylene-controlled processes in the hypocotyls of both light- and dark-grown seedlings. We show that BR biosynthesis is necessary for the formation of an exaggerated apical hook and that either application of BRs or disruption of BR synthesis alters auxin response, presumably by affecting auxin transport, eventually resulting in the disappearance of the apical hook. Furthermore, we demonstrate that ethylene-stimulated hypocotyl elongation in the light is largely controlled by the same mechanisms as those governing formation of the apical hook in darkness. However, in the light, BRs appear to compensate for the insensitivity to ethylene in hls mutants, supporting a downstream action of BRs. Hence, our results indicate that HLS1, SUR1/HLS3/RTY1/ALF1 and AMP1/HPT/COP2/HLS2/PT act on the auxin-ethylene interaction, rather than at the level of BRs. A model for the tripartite hormone interactions is presented.
[Show abstract][Hide abstract] ABSTRACT: Since the divergence of plants and animals about 1.5 billion yr ago, the signal transduction pathways in both kingdoms have
been subjected to very different selection pressures. These fundamental differences have influenced the evolution of both
the signaling molecules themselves and the mechanisms by which signals are relayed. Among these differences, a plant’s ability
to continuously form new organs during its postembryonic development, the increased frequency of high degrees of both ploidy
and gene duplication in many higher plants, and the multicellular haploid gametophytes of more primitive plants could be particularly
significant. Particular developmental processes, such as totipotency (the ability of a plant to regenerate itself from vegetative
tissue), have enabled plants to increase their reproductive potential and are consequences of the idiosyncrasies of a plant’s
cellular signaling mechanisms.
[Show abstract][Hide abstract] ABSTRACT: Polar transport-dependent local accumulation of auxin provides positional cues for multiple plant patterning processes. This directional auxin flow depends on the polar subcellular localization of the PIN auxin efflux regulators. Overexpression of the PINOID protein kinase induces a basal-to-apical shift in PIN localization, resulting in the loss of auxin gradients and strong defects in embryo and seedling roots. Conversely, pid loss of function induces an apical-to-basal shift in PIN1 polar targeting at the inflorescence apex, accompanied by defective organogenesis. Our results show that a PINOID-dependent binary switch controls PIN polarity and mediates changes in auxin flow to create local gradients for patterning processes.
[Show abstract][Hide abstract] ABSTRACT: STYLOSA (STY) in Antirrhinum and LEUNIG (LUG) in Arabidopsis control the spatially correct expression of homeotic functions involved in the control of floral organ identity. We show here that the sty mutant also displays alteration in leaf venation patterns and hypersensitivity towards auxin and polar auxin transport inhibitors, demonstrating that STY has a more general role in plant development. STY and LUG are shown to be orthologues that encode proteins with structural relation to GRO/TUP1-like co-repressors. Using a yeast-based screen we found that STY interacts with several transcription factors, suggesting that STY, like GRO/TUP1, forms complexes in vivo. Proteins of the YABBY family, characterised by containing a partial HMG domain, represent a major group of such interactors. In vivo association of STY with one of the YABBY proteins, GRAMINIFOLIA (GRAM), is supported by enhanced phenotypic defects in sty gram double mutants, for instance in the control of phyllotaxis, floral homeotic functions and organ polarity. Accordingly, the STY and GRAM protein and mRNA expression patterns overlap in emerging lateral organ primordia. STY is expressed in all meristems and later becomes confined to the adaxial domain and (pro)vascular tissue. This pattern is similar to genes that promote adaxial identity, and, indeed, STY expression follows, although does not control, adaxial fate. We discuss the complex roles of STY and GRAM proteins in reproductive and vegetative development, performed in part in physical association but also independently.
Development 09/2004; 131(15):3649-59. DOI:10.1242/dev.01205 · 6.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Suspension cultures from Arabidopsis thaliana wild type and AtPIN1-deficient lines were initiated and maintained for more than 3 years. A protocol for efficient regeneration from long-term suspension cultures was established. Arabidopsis wild-type and respectively AtPIN1 mutant plants have been regenerated from these cultures and characterized. Additionally, transgenic suspension cultures expressing the uidA ( -glucuronidase) reporter gene under the control of AtPIN1 promoter have been used for morphogenic studies. Our studies suggest that a lack of AtPIN1 function affects shoot differentiation and development, but does not influence in vitro regeneration of plants.
Plant Cell Tissue and Organ Culture 01/2004; 79(2):181-188. DOI:10.1007/s11240-004-0658-8 · 2.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) can stimulate hypocotyl elongation in light-grown Arabidopsis seedlings. A mutant, designated ACC-related long hypocotyl 1 (alh1), that displayed a long hypocotyl in the light in the absence of the hormone was characterized. Etiolated alh1 seedlings overproduced ethylene and had an exaggerated apical hook and a thicker hypocotyl, although no difference in hypocotyl length was observed when compared with wild type. Alh1 plants were less sensitive to ethylene, as reflected by reduction of ACC-mediated inhibition of hypocotyl growth in the dark and delay in flowering and leaf senescence. Alh1 also had an altered response to auxin, whereas auxin levels in whole alh1 seedlings remained unaffected. In contrast to wild type, alh1 seedlings showed a limited hypocotyl elongation when treated with indole-3-acetic acid. Alh1 roots had a faster response to gravity. Furthermore, the hypocotyl elongation of alh1 and of ACC-treated wild type was reverted by auxin transport inhibitors. In addition, auxin up-regulated genes were ectopically expressed in hypocotyls upon ACC treatment, suggesting that the ethylene response is mediated by auxins. Together, these data indicate that alh1 is altered in the cross talk between ethylene and auxins, probably at the level of auxin transport.
[Show abstract][Hide abstract] ABSTRACT: We have isolated, cloned and characterized a cDNA from Zea mays L., denoted ZmAP1, coding for an anionic peroxidase. The open reading frame of ZmAP1 starting 72 residues from the 5' end of the cDNA predicts a 37,778 dalton protein of 356 amino acid residues. The protein has high similarity to other peroxidases and contains two peroxidase motifs that carry two highly conserved histidines in the active center. We expressed recombinant ZmAP1 protein in E. coli as a fusion with maltose-binding protein. The fusion protein was biochemically active after addition of hemin to the apoprotein. The maize peroxidase ZmAP1 has a pH optimum at pH 4.0 and a Km of 0.2 mM for the substrate 2,2'-azino-bis-(3-ethyl-benzothiazolin-6-sulfonic acid) at this pH. In maize seedlings the ZmAP1 gene is expressed predominantly in roots, the mesocotyl, the coleoptile and to a lower extent in the node, whereas no expression in the primary leaf was found. In situ hybridization shows that the expression of ZmAP1 in the young maize root is confined to the epidermis, hypodermis and the pericycle.
European Journal of Biochemistry 09/1997; 247(3):826-32. DOI:10.1111/j.1432-1033.1997.00826.x · 3.58 Impact Factor