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A critical role for Arabidopsis MILDEW RESISTANCE LOCUS O2 in systemic acquired resistance
Author(s) -
Gruner Katrin,
Zeier Tatyana,
Aretz Christina,
Zeier Jürgen
Publication year - 2018
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/tpj.13920
Subject(s) - pseudomonas syringae , biology , mutant , arabidopsis , plant disease resistance , systemic acquired resistance , powdery mildew , gene , inoculation , microbiology and biotechnology , salicylic acid , locus (genetics) , genetics , botany , horticulture
Summary Members of the MILDEW RESISTANCE LOCUS O ( MLO ) gene family confer susceptibility to powdery mildews in different plant species, and their existence therefore seems to be disadvantageous for the plant. We recognized that expression of the Arabidopsis MLO 2 gene is induced after inoculation with the bacterial pathogen Pseudomonas syringae , promoted by salicylic acid ( SA ) signaling, and systemically enhanced in the foliage of plants exhibiting systemic acquired resistance ( SAR ). Importantly, distinct mlo2 mutant lines were unable to systemically increase resistance to bacterial infection after inoculation with P. syringae , indicating that the function of MLO 2 is necessary for biologically induced SAR in Arabidopsis. Our data also suggest that the close homolog MLO 6 has a supportive but less critical role in SAR . In contrast to SAR , basal resistance to bacterial infection was not affected in mlo2 . Remarkably, SAR ‐defective mlo2 mutants were still competent in systemically increasing the levels of the SAR ‐activating metabolites pipecolic acid (Pip) and SA after inoculation, and to enhance SAR ‐related gene expression in distal plant parts. Furthermore, although MLO 2 was not required for SA ‐ or Pip‐inducible defense gene expression, it was essential for the proper induction of disease resistance by both SAR signals. We conclude that MLO 2 acts as a critical downstream component in the execution of SAR to bacterial infection, being required for the translation of elevated defense responses into disease resistance. Moreover, our data suggest a function for MLO 2 in the activation of plant defense priming during challenge by P. syringae .