CmSGT1, Transcriptionally Regulated by CmWRKY21 and CmWRKY31, Improves Powdery Mildew Resistance in Cucurbita...

Powdery mildew (PM), mainly caused by Podosphaera xanthii, is a severe destructive disease that threatens the production of cucurbit crops globally. Heterologous transformation has shown that the CmSGT1 gene (suppressor of the G2 allele of skp1) improved PM resistance in tobacco. However, the function of the gene in pumpkins (Cucurbita moschata) is largely unknown. Herein, transient CmSGT1 overexpression in pumpkin cotyledons inhibited the spore germination and mycelia growth of P. xanthii by inducing an increase in salicylic acid (SA) content, and exogenous SA intensified the inhibitory effect of the gene on the growth of P. xanthii. The β-glucuronidase activity of cotyledons transformed with the CmSGT1 promoter was induced by PM and signaling molecules (gibberellic acid, ethephon, SA, abscisic acid, and methyl jasmonate). The yeast one-hybrid assay verified that transcription factor CmWRKY21, CmWRKY31, and CmWRKY75 proteins interact with the CmSGT1 promoter. Transactivation analysis revealed that CmWRKY21 and CmWRKY31 significantly triggered the expression of GUS driven by the CmSGT1 promoter under PM. Furthermore, transient co-overexpression of CmWRKY21/CmWRKY31 and CmSGT1 enhanced the inhibitory effect on the growth of P. xanthii. In conclusion, the CmSGT1 gene is a PM resistance gene in pumpkin and is transcriptionally regulated by CmWRKY21 and CmWRKY31. Our study provides a reference for resistance breeding of pumpkins.