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High humidity suppresses ssi4 ‐mediated cell death and disease resistance upstream of MAP kinase activation, H 2 O 2 production and defense gene expression
Author(s) -
Zhou Fasong,
Menke Frank L.H.,
Yoshioka Keiko,
Moder Wolfgang,
Shirano Yumiko,
Klessig Daniel F.
Publication year - 2004
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2004.02180.x
Subject(s) - biology , mutant , wrky protein domain , kinase , plant disease resistance , signal transduction , gene , microbiology and biotechnology , arabidopsis , genetics
Summary The Arabidopsis ssi4 mutant, which exhibits spontaneous lesion formation, constitutive expression of pathogenesis‐related ( PR ) genes and enhanced resistance to virulent bacterial and oomycete pathogens, contains a gain‐of‐function mutation in a TIR‐NBS‐LRR type R gene. Epistatic analyses revealed that both PR gene expression and disease resistance are activated via a salicylic acid (SA)‐ and EDS1 ‐dependent, but NPR1 ‐ and NDR1 ‐independent signaling pathway. In this study, we demonstrate that in moderate relative humidity (RH; 60%), the ssi4 mutant accumulates H 2 O 2 and SA prior to lesion formation and displays constitutive activation of the MAP kinases AtMPK6 and AtMPK3. It also constitutively expresses a variety of defense‐associated genes, including those encoding the WRKY transcription factors AtWRKY29 and AtWRKY6, the MAP kinases AtMPK6 and AtMPK3, the powdery mildew R proteins RPW8.1 and RPW8.2, EDS1 and PR proteins. All of these ssi4 ‐induced responses, as well as the chlorotic, stunted morphology and enhanced disease resistance phenotype, are suppressed by high RH (95%) growth conditions. Thus, a humidity sensitive factor (HSF) appears to function at an early point in the ssi4 signaling pathway. All ssi4 phenotypes, except for MAP kinase activation, also were suppressed by the eds1‐1 mutation. Thus, ssi4 ‐induced MAP kinase activation occurs downstream of the HSF but either upstream of EDS1 or on a separate branch of the ssi4 signaling pathway. SA is a critical signaling component in ssi4 ‐mediated defense responses. However, exogenously supplied SA failed to restore lesion formation in high RH‐grown ssi4 plants, although it induced defense gene expression. Thus, additional signals also are involved.