Transcription factor WRKY23 assists auxin distribution patterns during Arabidopsis root development through local control on flavonol biosynthesis

Abstract

Gradients of the plant hormone auxin, which depend on its active intercellular transport, are crucial for the maintenance of root meristematic activity. This directional transport is largely orchestrated by a complex interaction of specific influx and efflux carriers that mediate the auxin flow into and out of cells, respectively. Besides these transport proteins, plant-specific polyphenolic compounds known as flavonols have been shown to act as endogenous regulators of auxin transport. However, only limited information is available on how flavonol synthesis is developmentally regulated. Using reduction-of-function and overexpression approaches in parallel, we demonstrate that the WRKY23 transcription factor is needed for proper root growth and development by stimulating the local biosynthesis of flavonols. The expression of WRKY23 itself is controlled by auxin through the AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 transcriptional response pathway. Our results suggest a model in which WRKY23 is part of a transcriptional feedback loop of auxin on its own transport through local regulation of flavonol biosynthesis.flavonoid | lateral root | WRKY P lant growth and development are characterized by recurrent organogenesis and continuous adaptation to environmental conditions. These intriguing features rely on the ability to establish and maintain meristematic activity. Both de novo induction and maintenance of root meristematic activity are governed by gradients of the plant hormone auxin (1-3). Although several plant tissues are able to synthesize auxin (4, 5), installation and maintenance of auxin maxima are mediated mainly by polar auxin transport (6). Besides the well-known auxin import (AUXIN RESISTANT 1/LIKE AUX1) and export (PIN-FORMED [PIN] and ABCB/P-GLYCOPROTEIN/MDR) proteins (7-10), additional regulators mediate the flow of auxin throughout the plant. For example, flavonols (plant-specific polyphenolic compounds), have been proposed to act as endogenous auxin transport regulators based on their competition with the synthetic auxin transport inhibitor 1-N-naphthylphthalamic acid (11). Although the molecular targets of flavonol regulation remain unknown, genetic and pharmacologic evidence clearly demonstrate a role for these secondary metabolites as negative regulators of auxin transport (12-18). Flavonol biosynthesis was recently shown to be induced by auxin through a TRANSPORT INHIBITOR RESPONSE 1 (TIR1) auxin receptor-dependent pathway (16). However, our understanding of how flavonol biosynthesis is fine-tuned during development and in response to internal and environmental signals is still limited. Here, we report on the functional characterization of a member of the WRKY family, a large, plant-specific class of transcription factors that has been associated with responses to pathogen attack, mechanical stress, and senescence (19). Our results suggest that proper expression of WRKY23 is essential for normal root development, and that misexpression of WRKY23 causes defects in meristem organization by inte...

The WRKY Transcription Factor WRKY71/EXB1 Controls Shoot Branching by Transcriptionally Regulating RAX Genes in Arabidopsis

“…In this article, we found that the auxin pathway was compromised in the exb1-D mutant, as shown by auxin reporter DR5-GUS analysis and by the reduced rates of hypocotyl elongation of exb1-D in high temperature treatment. This is consistent with the fact that overexpression of WRKY23 disrupts auxin transport and response (Grunewald et al, 2012). Auxin is a well-known inhibitor of bud outgrowth and an auxin minimum is required for AM initiation (Hayward et al, 2009;Stirnberg et al, 2012;Y.…”

“…WRKY23 acts downstream of IAA14, AUXIN RESPONSE FACTOR7 (ARF7), and ARF19 (Grunewald et al, 2008(Grunewald et al, , 2012. WRKY23 also controls auxin distribution by regulating flavonol biosynthesis during plant root and embryo development (Grunewald et al, 2012(Grunewald et al, , 2013. In this article, we found that the auxin pathway was compromised in the exb1-D mutant, as shown by auxin reporter DR5-GUS analysis and by the reduced rates of hypocotyl elongation of exb1-D in high temperature treatment.…”

“…WRKY57 affects auxin signaling by interacting with AUX/IAA protein IAA29 in the regulation of jasmonate-induced leaf senescence (Jiang et al, 2014). WRKY23 acts downstream of IAA14, AUXIN RESPONSE FACTOR7 (ARF7), and ARF19 (Grunewald et al, 2008(Grunewald et al, , 2012. WRKY23 also controls auxin distribution by regulating flavonol biosynthesis during plant root and embryo development (Grunewald et al, 2012(Grunewald et al, , 2013.…”

Flavonoids and Auxin Transport Inhibitors Rescue Symbiotic Nodulation in the Medicago truncatula Cytokinin Perception Mutant cre1

“…Similarly, auxin transport phenotypes in several Arabidopsis flavonoid mutants have been linked to altered accumulation of flavonoid glycosides as they contain undetectable levels of free kaempferol or quercetin aglycones (Buer et al, 2013). In addition, overexpression of the transcription factor WRKY23 in Arabidopsis led to increased levels of quercetin-3-O-rhamnoside, accompanied by a reduced auxin transport in seedling roots (Grunewald et al, 2012). Among the 18 cytokinin-inducible flavonoid-related genes, 14 were putative (iso)flavonoid glycosyl transferases (Ariel et al, 2012;Supplemental Table 2).…”

Identification of key genes involved in root development of tomato using expressed sequence tag analysis

“…However, some of the genes belongs to WRKY and myb gene family, known to take part in root development, were found in root specific library. WRKY is required for the growth of roots by stimulating synthesis of flavonols, an endogenous regulators of auxin transport (Grunewald et al 2012) and later has a role in root growth of legumes (Volpe et al 2013). In contrast, a gene encoding for Lysine-specific histone demethylase (KDM1), which is involved in transcriptional repression of root genes via demethylation of histones was also identified in ESTs library probably required for tight regulation of temporal genes (Krichevsky et al 2011).…”