Replication-associated protein A (RepA), encoded by the citrus chlorotic dwarf-associated virus (CCDaV), can activate cell death in the non-host plant Nicotiana benthamiana. However, it remains unknown whether and how it induces immune responses in its citrus host. In this study, we found that RepA overexpression in Eureka lemon enhanced resistance to CCDaV and concomitantly increased jasmonic acid (JA) content. Further study suggested that both JA and its key biosynthetic gene ClAOS positively regulated the antiviral resistance. In addition, yeast one-hybrid and dual-luciferase reporter assay confirmed that RepA functions as a transcription factor, directly binding to the ClAOS promoter to activate its transcription. Collectively, these results delineate how the geminiviral protein transcriptionally reprogrammes host defence metabolism, providing new insights into the modulation of plant immunity by virus-encoded proteins.
Zhao et al. (Sun,) studied this question.