CtChi19: a valuable gene for improving resistance to Botrytis cinerea and Alternaria alternata in Carthamus tinctorius.

Safflower (Carthamus tinctorius L.) is an economically important crop with both medicinal and oil-producing values, However, its production is severely threatened by fungal diseases, including those caused by Alternaria alternata and other pathogenic fungi. To date, molecular investigations into the disease resistance mechanisms of safflower remain largely limited. In this study, proteomic analysis was performed on safflower following infection by A. alternata, identifying 490 and 921 differentially expressed proteins (DEPs) at 48 hours post-infection (hpi) and 72 hpi, respectively, Among these DEPs, a large number of candidate defense-related proteins were detected, including CtChi19. Meanwhile, by integrating previously published transcriptomic and proteomic data of safflower at the early stage of Botrytis cinerea infection, a set of candidate genes closely associated with defense responses was screened using weighted gene co-expression network analysis (WGCNA). Emphasis was placed on the hub gene CtChi19, which encodes a chitinase belonging to glycoside hydrolase family 19 (GH19). Subcellular localization assays showed that CtChi19 was localized in the cell wall and extracellular space. Furthermore, stable overexpression of CtChi19 in safflower significantly enhanced the resistance of transgenic plants to both B. cinerea and A. alternata. Assays of chitinase and β-1,3-glucanase activities demonstrated that the improved disease resistance of OE-CtChi19 transgenic plants was directly associated with a significant increase in chitinase and β-1,3-glucanase activities. Collectively, the candidate genes identified in this study provide valuable genetic resources and theoretical support for molecular breeding aimed at developing disease-resistant safflower varieties. These findings also offer novel insights for further dissecting the antifungal immune mechanisms in safflower.