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

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 .