High Temperature Promoted the Accumulation of Citrus Yellow Mosaic Virus in Citrus sinensis via Weakening the Immune Function of the CsWRKY76-CsPR4A Modules.

Rising global temperatures exacerbate the severity of crop diseases, threatening global agricultural production. Citrus yellow mosaic virus (CYMV) is one of the pathogens that seriously threaten citrus production, the world's largest fruit industry. However, the molecular mechanisms underlying CYMV-citrus interactions at high temperatures remain poorly understood. Over a 1-year observation period, this study found elevated temperatures increased CYMV accumulation in Madam Vinous sweet orange. Controlled experiments comparing 25°C and 37°C conditions further validated this phenomenon, with significantly higher viral titres observed under high-temperature treatments (37°C). Subsequent transcriptomic analysis revealed that the transcription factor CsWRKY76 and the pathogenesis-related gene CsPR4A were significantly downregulated in sweet orange infected with CYMV at 37°C. CsWRKY76 could directly bind to the CsPR4A promoter, thereby positively regulating CsPR4A transcription. Overexpression of CsWRKY76 or CsPR4A in transgenic citrus hairy roots significantly suppressed CYMV accumulation, while RNAi-mediated silencing of either gene promoted viral accumulation, indicating that both genes were positive regulators of citrus immunity. Overexpression of CsWRKY76 increased hydrogen peroxide content in transgenic citrus hairy roots while upregulating CsPAL2 and CsCOMT1 (involved in phenylpropanoid metabolism). This study elucidates the molecular mechanism by which high temperature suppresses the immune function of the CsWRKY76-CsPR4A modules and thereby promotes the accumulation of CYMV. Our results provide a theoretical basis for developing high-temperature-resistant disease control strategies in citrus.