Positively Regulates -Mediated Immunity in .

Ectopic expression of the Arabidopsis () boosts pattern-triggered immunity leading to enhanced resistance to different pathogens in Arabidopsis and rice. However, the underlying regulatory mechanism remains largely elusive. Here, we report that () positively regulates -mediated cell death and disease resistance. Forward genetic screen identified the mutant that exhibited less cell death and susceptibility to powdery mildew and bacterial pathogens. Map-based cloning identified a G-to-A point mutation at the 3' splice site of the 8th intron, which resulted in splice shift to 8-bp down-stream of the original splice site of in , and introduced into a stop codon after two codons leading to a truncated XCT. has previously been identified as a circadian clock gene required for small RNA biogenesis and acting down-stream of () in the ethylene-signaling pathway. Here we further showed that mutation or down-regulation of by artificial microRNA reduced -mediated immunity in R1Y4, a transgenic line expressing from the native promoter. On the contrary, overexpression of in R1Y4 background enhanced -mediated cell death, HO production and resistance against powdery mildew. Consistently, the expression of was down- and up-regulated in mutant and overexpression lines, respectively. Taken together, these results indicate that positively regulates -mediated cell death and disease resistance, and provide new insight into the regulatory mechanism of -mediated immunity.