The mutant STAY-GREEN () in cucumber interacts with the CSEP30 protein to elicit a defense response against .

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Disease-resistant plants activate immune responses by specifically recognition Candidate Secreted Effector Proteins (CSEPs) through resistance (R) proteins. In research on cucumber powdery mildew resistance breeding, several R genes and CSEPs have been identified; however, the specific interactions between R proteins and CSEPs are still largely unexplored. In this study, we used a luciferase reporter assay to identify six CSEPs from that potentially induce cell death in cucumber. Subsequent yeast two-hybrid analysis revealed that only the mature form of CSEP30 (CSEP30) interacted with the cucumber mutant STAY-GREEN (), a gene previously recognized for its broad-spectrum resistance in genetic studies. This interaction was confirmed using pull-down and co-immunoprecipitation assays. Additionally, to determine if the interaction leads to phenotypic changes, Cssgr and CSEP30 were transiently expressed in tobacco leaves. The infiltration of Cssgr in tobacco resulted in reduced chlorosis compared to the wild-type CsSGR. Co-infiltration of Cssgr with CSEP30 induced distinct dry necrotic lesions, contrasting the effects observed when Cssgr and CSEP30 were infiltrated separately. Additionally, after infection in moderately powdery mildew-resistant Gy14 cucumber, similar necrotic lesions and specific expression of , as along with defense response-related genes (), were observed. This study suggests that the interaction between Cssgr and CSEP30 could trigger cell death and defense response, offering new insights into the molecular function of Cssgr in disease resistance in Gy14 cucumber.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11032-024-01504-6.