Divergent symptoms caused by geminivirus-encoded C4 proteins correlate with their ability to bind NbSKη.

Geminiviruses induce severe developmental abnormalities in plants. The C4/AC4 protein encoded by geminiviruses, especially by those not associated with betasatellites, functions as a symptom determinant through hijacking a shaggy-related protein kinase (SKη) and interfering with its functions. Here, we report that the symptom determinant capability of C4 proteins encoded by different geminiviruses is divergent and tightly correlated with their ability to interact with SKη from Nicotiana benthamiana (NbSKη). Swap of the mini-domain of tomato leaf curl Yunnan virus (TLCYnV) C4 critical for the interaction with NbSKη increased the capacity of the C4 proteins encoded by tomato yellow leaf curl China virus (TYLCCNV) or tobacco curly shoot virus (TbCSV) to induce symptoms. The severity of symptoms induced by recombinant TYLCCNV C4 or TbCSV C4 correlates with the amount of NbSKη tethered to the plasma membrane by the viral protein. Moreover, a recombinant TYLCCNV harboring the mini-domain of TLCYnV C4 induces more severe symptoms than wild-type TYLCCNV. Thus, this study provides new insights into the mechanism by which different geminivirus-encoded C4 proteins possess divergent symptom determinant capabilities.IMPORTANCE Geminiviruses constitute the largest group of known plant viruses and cause devastating diseases in many economically important crops world-wide. Geminivirus encoded C4 protein is a multifunctional protein. In this study, we found that the C4 proteins from different geminiviruses showing a differential ability to interact with NbSKη, which correlated with their symptom determinant capability. Moreover, a mini-domain of tomato leaf curl Yunnan virus (TLCYnV) C4 indispensable for interacting with NbSKη and tethering it to the plasma membrane to lead to symptom induction was determined. Supporting to these, a recombinant geminivirus carrying the mini-domain of TLCYnV C4 induced more severe symptoms than its original one. Therefore, these findings expand the scope of the interaction of NbSKη and C4-mediated symptom induction and contribute to further understanding of the multiple roles of C4.