Targets of AtWRKY6 regulation during plant senescence and pathogen defense

Abstract

In Arabidopsis, WRKY factors comprise a large gene family of plant-specific transcriptional regulators controlling several types of plant stress responses. To understand the regulatory role of WRKY proteins during such processes, we identified targets of the senescence-and defense-associated WRKY6 factor. WRKY6 was found to suppress its own promoter activity as well as that of a closely related WRKY family member, indicating negative autoregulation. On the other hand, WRKY6 positively influenced the senescence-and pathogen defense-associated PR1 promoter activity, most likely involving NPR1 function. One novel identified target gene, SIRK, encodes a receptor-like protein kinase, whose developmental expression is strongly induced specifically during leaf senescence. The transcriptional activation of SIRK is dependent on WRKY6 function. Senescing leaves of wrky6 knockout mutants showed a drastic reduction, and green leaves of WRKY6 overexpression lines showed clearly elevated SIRK transcript levels. Furthermore, the SIRK gene promoter was specifically activated by WRKY6 in vivo, functioning very likely through direct W-box interactions.

Large‐scale identification of leaf senescence‐associated genes

“…The SSH method, which has proved to be a powerful tool for the ampli®cation of non-abundant transcripts in other systems (Diatchenko et al, 1999), allowed us to identify a number of new SAGs encoding potential regulators. In addition to the two reported senescence-related receptors, senescence-associated receptor kinase (SARK; Hajouj et al, 2000) and senescence-induced receptor kinase (SIRK; Robatzek and Somssich, 2002), we revealed in our screen a cDNA clone that represents a receptor-like protein kinase (At5g48380). Other mRNAs for signal transduction components preferentially accumulated as leaves senesce are represented by the clones encoding a small GTP-binding protein (At5g47201), related to the oncogene RAS and a G protein beta subunit-like protein (At2g43770).…”

“…Recently, a few senescence-associated regulatory genes have been identi®ed. They are predicted to encode transcription factors (Eulgem et al, 2000;Hinderhofer and Zentgraf, 2001;Robatzek and Somssich, 2002), receptors for senescence perception (Hajouj et al, 2000;Robatzek and Somssich, 2002), and components of intracellular protein traf®cking (Guterman et al, 2003). Among the genes that are upregulated during leaf senescence are several whose transcript levels accumulate also under abiotic and biotic stresses (Binyamin et al, 2000;Hanfrey et al, 1996;John et al, 1997;Quirino et al, 1999;Weaver et al, 1998).…”

An extensive microarray analysis of AAL-toxin-induced cell death in Arabidopsis thaliana brings new insights into the complexity of programmed cell death in plants

“…The members of this family (74 in Arabidopsis) have diverse biological functions ranging from stress responses to development [36]. Interestingly, the two developmental processes in which WRKY transcription factors are implicated are trichome development and senescence, and in both cases PCD is indispensable for the normal processes to occur [37,38]. In contrast with WRKYs, the involvement of DREB-like AP2 domain transcription factor and NAM transcription factors in PCD is not clear.…”

The rice transcription factor OsWRKY47 is a positive regulator of the response to water deficit stress

“…Atwrky6 knockout mutants showed a drastic growth reduction, and AtWRKY6 overexpression led to increased SIRK expression. Notably, the SIRK promoter comprises a W-box indicating a direct activation by WRKY6 in vivo (Robatzek and Somssich 2002). WRKY53 has been related to senescence and several target genes, among these, other WRKY TFs, senescence-associated genes and others similar to the putatve OsWRKY47 targets, indicating similar functions of these Arabidopsis and rice TFs.…”