MYB46 Modulates Disease Susceptibility to Botrytis cinerea in Arabidopsis    

Abstract

In this study, we show that the Arabidopsis (Arabidopsis thaliana) transcription factor MYB46, previously described to regulate secondary cell wall biosynthesis in the vascular tissue of the stem, is pivotal for mediating disease susceptibility to the fungal pathogen Botrytis cinerea. We identified MYB46 by its ability to bind to a new cis-element located in the 5# promoter region of the pathogen-induced Ep5C gene, which encodes a type III cell wall-bound peroxidase. We present genetic and molecular evidence indicating that MYB46 modulates the magnitude of Ep5C gene induction following pathogenic insults. Moreover, we demonstrate that different myb46 knockdown mutant plants exhibit increased disease resistance to B. cinerea, a phenotype that is accompanied by selective transcriptional reprogramming of a set of genes encoding cell wall proteins and enzymes, of which extracellular type III peroxidases are conspicuous. In essence, our results substantiate that defense-related signaling pathways and cell wall integrity are interconnected and that MYB46 likely functions as a disease susceptibility modulator to B. cinerea through the integration of cell wall remodeling and downstream activation of secondary lines of defense.

Arabidopsis Defense against Botrytis cinerea: Chronology and Regulation Deciphered by High-Resolution Temporal Transcriptomic Analysis

“…Consistent with reduction in activity of these genes leading to activation of defense signaling, CeSA1 and CeSA3 are downregulated during B. cinerea infection. Knockouts of a secondary cell wall regulator, MYB46, were recently shown to be less susceptible to B. cinerea (Ramírez et al, 2011a). Downregulation of six cellulase synthase genes (including CeSA1 and CeSA3) following B. cinerea infection occurs more rapidly and to a greater degree in myb46 knockout lines compared with the wild type (Ramírez et al, 2011b), suggesting the timing of CeSA repression may be crucial.…”

“…The motif was identified as the binding site for MYB80; however, neither MYB80 nor the six other MYBs most closely related to MYB80 are differentially expressed after B. cinerea infection, suggesting other MYB TFs may be involved. Several members of the MYB family have regulatory roles in response to biotic stress (Mengiste et al, 2003;Clay et al, 2009;Ramírez et al, 2011a), and 36 of the 132 MYB TFs in Arabidopsis (Stracke et al, 2001) are differentially expressed in response to B. cinerea infection.…”

“…Expression of several of these, including ERF1, ERF5, ERF6, RAP2.2, and ORA59, influences host susceptibility to B. cinerea, with ERF5 a key component of chitinmediated immunity (Berrocal-Lobo et al, 2002;Pré et al, 2008;Moffat et al, 2012;Son et al, 2012;Zhao et al, 2012). Members of the MYB and NAC families (Wang et al, 2009;Ramírez et al, 2011a) have also been shown to influence plant susceptibility to B. cinerea.…”

MED18 interaction with distinct transcription factors regulates multiple plant functions

“…Notably, plant pathogen resistance mechanisms and the transcriptional activation of defence-related genes vary depending on the nature of the pathogen and their virulence mechanisms 12 . Arabidopsis WRKY33, BOS1 (BOTRYTIS SUSCEPTIBLE 1) and RAP2.2 are examples of TFs that promote resistance 13-15, whereas MYB44 and MYB46 suppress resistance to fungal necrotrophs 16 . TFs are also controlled by their co-activators and post-transcriptional regulatory mechanisms.…”

ATL54, a ubiquitin ligase gene related to secondary cell wall formation, is transcriptionally regulated by MYB46

“…This result indicates that MYB46 can bind to multiple sites in the ATL54 promoter. Recently, several researchers have proposed MYB46-binding elements such as MBSII (GTTAGGT; Ramírez et al 2011) Kim et al 2012], and SMRE [ACC(A/ T) A(A/C)(T/C); Zhong and Ye 2012]. We found three distinct motifs similar to these proposed MYB46-binding elements in the ATL54 promoter region used in EMSA (−163 to −662; see Supplemental Figure S1).…”