Functional Analysis of MYB73 of Arabidopsis thaliana Against Bipolaris oryzae

Bipolaris oryzae is a severe rice disease, resulting in significant economic losses. MYB73 gene of Arabidopsis was isolated based on T-DNA insertion mutants whose lose-of-function mutant increased susceptibility to B. oryzae. Results of staining for H2O2 revealed that infection of incompatible B. oryzae caused much more strong brown patches on the leaves of myb73 mutant than those on the leaves of wild type. Expression of MYB73 gene was induced by B. oryzae. Its increased expression was severely impaired in the myb73 mutant. Expression of MYB73 was severely decreased in the npr1, jar1, eds5, and sid2 mutants, suggesting MYB73 gene participates in the jasmonate (JA) and salicylic acid (SA) signaling pathways. Expression of MYB73 who encoded an R2R3 MYB transcription factor was increased by SA, JA, and ethylene (ET) treatments. The cDNA full-length sequence of MYB73 was 960 bp and a protein with 320 amino acids was encoded. The predicted molecular weight of MYB73 was 34.85 kDa. The expression of MYB73 gene was induced within 24 h of the inoculation, however, the expression of PR1, PDF1.2 and NPR1 weren't changed. When B. oryzae successfully infected myb73 mutant plants, the expression of PR1, PDF1.2 and NPR1 were increased. Collectively, our results suggested that MYB73 is involved in NPR1-mediated SA and JA signaling pathways.