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Drought-acclimated Arabidopsis plants have increased bacterial disease resistance that requires a functional RD21A

Kunru Wang: Virginia Tech

<div>As one major abiotic stress, drought could significantly reduce crop yields. It has recently been revealed that drought stress also has a strong influence on the plant immunity. However, the molecular mechanism of the drought-regulated immunity has not been well studied. We demonstrated that drought-induced gene <em>RD21A,</em> encodes a cysteine protease, which plays a key role in the drought-induced immunity. The well-watered wild type <em>Arabidopsis</em> (Col-0) plants were more susceptible to a coronatine defective strain DB29 of <em>Pseudomonas syringae</em> pv. <em>tomato</em> DC3000 (<em>Pst</em>-DC3000(DB29)) than that have a temporary drought treatment. However, this drought-induced defense was compromised in the <em>rd21a</em> mutant background. Yeast two-hybrid and co-immunoprecipitation assays uncovered that RD21A interacts with ubiquitin E3 ligase SINAT4. Transient expression results indicated that RD21A could be degraded by SINAT4 <em>in vivo</em>. Consistent with the phenotype of null mutant <em>rd21a</em>, the overexpression of SINAT4 also compromised the drought-induced immunity to <em>Pst</em>-DC3000 (DB29). Furthermore, we also demonstrated that bacterial type III effector AvrRxo1 delivered by<em> Pst</em>-DC3000 (DB29) interacts with both SINAT4 and RD21A <em>in vivo</em>. Protease enzyme assays demonstrated that AvrRxo1 could enhance the E3 enzyme activity of SINAT4, and facilitate the degradation of RD21A <em>in vivo</em>. These results highlight RD21A has a key role in the drought-induced immunity, which can also be targeted by the pathogen virulence effectors.</div>