A geminivirus AC5 protein interacts with plant hormonal signalling and impacts plant defence

Geminiviruses are a large group of plant viruses responsible for yield loss in various crops, mainly in the tropical and sub-tropical regions. Geminiviruses encode six to nine multifunctional proteins, which interact with plant components to cause pathogenesis. One of the least studied geminiviral proteins is AC5. This study presents the first evidence of an AC5 protein interacting with a component of the abscisic acid signalling pathway, resulting in a depressed state. We show that the AC5 protein, encoded by Sri Lankan cassava mosaic virus is important for symptom development and virus accumulation in the experimental host Nicotiana benthamiana. The above interaction perturbs the abscisic acid signalling pathways, leading to compromised expression of defense-related genes and insensitivity to abscisic acid in transgenic Arabidopsis plants. This suggests a novel role of AC5 to facilitate virus propagation. Furthermore, we show that transiently suppressing the expression in N. benthamiana PP2C with which AC5 interacts, results in a reduction in viral titers possibly due to augmented ABA signaling and its defense-related roles. This research provides valuable insights into how geminiviral proteins manipulate ABA-mediated defence pathways, paving the way for further investigation into the underlying mechanisms and potential applications in plant protection against viral infections.