P-348 - An endocytic pathway mediates plasma membrane-to-chloroplast protein trafficking to regulate defence

Viruses possess highly compact genomes and only encode a limited number of proteins. However, viruses are capable of colonizing their hosts, suggesting that viral proteins engage in complex and sophisticated interactions with host components to evade plant defense. Therefore, harnessing viruses to explore uncharted cellular defensive pathways represents a fascinating and promising research direction. Here, using the tomato yellow leaf curl virus-encoded C4 protein, which has been demonstrated to localize to both the plasma membrane (PM) and chloroplasts, as a probe, we identified a novel endocytosis-mediated protein trafficking pathway that transports proteins from the PM to chloroplasts upon biotic stress to inhibit salicylic acid synthesis. Further validation using the plant calcium protein kinase 16 (CPK16) protein demonstrates that this uncharacterized pathway transports host proteins and has been co-opted by geminiviruses. TurboID-based proximity labelling revealed a series of key components involved in this pathway, specifically labeled by both the C4 and CPK16 proteins in Nicotiana benthamiana. Functional enrichment analysis and in vivo biochemical and cell biology assays suggest that ubiquitination may play a key regulatory role in the initiation of this intracellular trafficking. Taken together, our findings expand the current understanding of canonical endocytosis and provide new insights into PM-to-organelle communication in plant defence.