Rice OsAAA-ATPase1 is Induced during Blast Infection in a Salicylic Acid-Dependent Manner, and Promotes Blast Fungus Resistance

Abstract

Fatty acids (FAs) have been implicated in signaling roles in plant defense responses. We previously reported that mutation or RNAi-knockdown (<i>OsSSI2</i>-kd) of the rice <i>OsSSI2</i> gene, encoding a stearoyl acyl carrier protein FA desaturase (SACPD), remarkably enhanced resistance to blast fungus <i>Magnaporthe oryzae</i> and the leaf-blight bacterium <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>). Transcriptomic analysis identified six AAA-ATPase family genes (hereafter <i>OsAAA-ATPase1-6</i>) upregulated in the <i>OsSSI2</i>-kd plants, in addition to other well-known defense-related genes. Here, we report the functional analysis of <i>OsAAA-ATPase1</i> in rice's defense response to <i>M. oryzae</i>. Recombinant OsAAA-ATPase1 synthesized in <i>Escherichia coli</i> showed ATPase activity. <i>OsAAA-ATPase1</i> transcription was induced by exogenous treatment with a functional analogue of salicylic acid (SA), benzothiadiazole (BTH), but not by other plant hormones tested. The transcription of <i>OsAAA-ATPase1</i> was also highly induced in response to <i>M. oryzae</i> infection in an SA-dependent manner, as gene induction was significantly attenuated in a transgenic rice line expressing a bacterial gene (<i>nahG</i>) encoding salicylate hydroxylase. Overexpression of <i>OsAAA-ATPase1</i> significantly enhanced pathogenesis-related gene expression and the resistance to <i>M. oryzae</i>; conversely, RNAi-mediated suppression of this gene compromised this resistance. These results suggest that <i>OsAAA-APTase1</i> plays an important role in SA-mediated defense responses against blast fungus <i>M. oryzae</i>.