Abstract

Potato late blight, caused by Phytophthora infestans , severely affects the yield and quality of potatoes worldwide. Previous studies have demonstrated that suppressing abscisic acid (ABA) synthesis triggers a defense response against late blight. In this study, potatoes treated with fluorochloridone (Flu), an inhibitor of carotenoid- a precursor in the ABA biosynthesis pathway-exhibited enhanced defense against late blight under both field and greenhouse conditions. RNA sequencing analysis revealed that Flu treatment upregulated 229 genes and downregulated 212 genes in potatoes. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of ten randomly selected differentially expressed genes (DEGs) confirmed that the qRT-PCR data were consistent with the RNA sequencing results. Among the DEGs, 17 genes were upregulated, and 9 genes were downregulated in response to copper ions. Phytohormone analysis indicated that Flu treatment decreased ABA levels while increasing salicylic acid (SA) levels in potatoes. Notably, StWRKY40 is a marker gene activated by SA and functions downstream of SA. Furthermore, overexpression of StWRKY40 enhanced potato resistance to late blight, whereas knockdown of StWRKY40 promoted susceptibility to P. infestans. These results demonstrated that StWRKY40 plays a pivotal role in the Flu-activated defense response to late blight. SA treatment also protected potatoes against late blight under both field and greenhouse conditions. Overall, this study provides evidence supporting a model in which StWRKY40 is essential for Flu-mediated immune responses in potatoes.