At MYB 44 regulates WRKY 70 expression and modulates antagonistic interaction between salicylic acid and jasmonic acid signaling

Abstract

Summary: The role of A t MYB 44, an R 2 R 3 MYB transcription factor, in signaling mediated by jasmonic acid (JA) and salicylic acid (SA) is examined. A t MYB 44 is induced by JA through CORONATINE INSENSITIVE 1 (COI 1). A t MYB 44 over‐expression down‐regulated defense responses against the necrotrophic pathogen A lternaria brassicicola, but up‐regulated WRKY 70 and PR genes, leading to enhanced resistance to the biotrophic pathogen P seudomonas syringae pv. tomato DC 3000. The knockout mutant atmyb44 shows opposite effects. Induction of WRKY 70 by SA is reduced in atmyb44 and npr1‐1 mutants, and is totally abolished in atmyb44 npr1‐1 double mutants, showing that WRKY 70 is regulated independently through both NPR 1 and A t MYB 44. At MYB 44 over‐expression does not change SA content, but A t MYB 44 over‐expression phenotypes, such as retarded growth, up‐regulated PR 1 and down‐regulated PDF 1.2 are reversed by SA depletion. The wrky70 mutation suppressed At MYB 44 over‐expression phenotypes, including up‐regulation of PR 1 expression and down‐regulation of PDF 1.2 expression. β‐estradiol‐induced expression of A t MYB 44 led to WRKY 70 activation and thus PR 1 activation. A t MYB 44 binds to the WRKY 70 promoter region, indicating that A t MYB 44 acts as a transcriptional activator of WRKY 70 by directly binding to a conserved sequence element in the WRKY 70 promoter. These results demonstrate that A t MYB 44 modulates antagonistic interaction by activating SA‐mediated defenses and repressing JA‐mediated defenses through direct control of WRKY 70.