Find in Library

Rice plants contain high basal levels of salicylic acid (SA), but some of their functions remain elusive. To elucidate the importance of SA homeostasis in rice immunity, we characterized four rice SA hydroxylase genes (<i>OsSAHs</i>) and verified their roles in SA metabolism and disease resistance. Recombinant OsSAH proteins catalyzed SA in vitro, while OsSAH3 protein showed only SA 5-hydroxylase (SA5H) activity, which was remarkably higher than that of other OsSAHs that presented both SA3H and SA5H activities. Amino acid substitutions revealed that three amino acids in the binding pocket affected SAH enzyme activity and/or specificity. Knockout <i>OsSAH</i><i>2</i> and <i>OsSAH3</i> (<i>sah</i>KO) genes conferred enhanced resistance to both hemibiotrophic and necrotrophic pathogens, whereas overexpression of each <i>OsSAH</i> gene increased susceptibility to the pathogens. <i>sah</i>KO mutants showed increased SA and jasmonate levels compared to those of the wild type and <i>OsSAH</i>-overexpressing plants. Analysis of the <i>OsSAH3</i> promoter indicated that its induction was mainly restricted around <i>Magnaporthe oryzae</i> infection sites. Taken together, our findings indicate that SA plays a vital role in immune signaling. Moreover, fine-tuning SA homeostasis through suppression of SA metabolism is an effective approach in studying broad-spectrum disease resistance in rice.