Stability of Begomoviral pathogenicity determinant βC1 is modulated by mutually antagonistic SUMOylation and SIM interactions

Abstract

To successfully invade new hosts, to break host resistance as well as to move within and between plant cells, viruses and their satellites have evolved a coordinated network of protein interactions. {beta}C1 protein encoded by specific geminiviral satellites acts as a key pathogenicity determinant. {beta}C1 from diverse viruses undergo multiple post-translational modifications (PTMs) such as ubiquitination and phosphorylation. However, the relevance of these and other layers of PTMs in host-geminiviral interactions has not been fully understood. Here we identified the significance of a novel layer of PTMs in Synedrella yellow vein clearing virus (SyYVCV) encoded {beta}C1 protein having well conserved SUMOylation and SUMO-interacting motifs (SIMs). We observed that SyYVCV {beta}C1 undergoes SUMOylation in host plants as a defensive strategy against ubiquitin mediated degradation. On the contrary, SIMs encoded in {beta}C1 mediate degradation of {beta}C1. Both these PTMs are also essential for the function of {beta}C1 protein since SIM and SUMOylation motif mutants failed to promote pathogenicity and viral replication in vivo. In addition, SUMOylation in different motifs of {beta}C1 led to functionally distinct outcomes, regulating the stability and function of the {beta}C1 protein, as well as increased global SUMOylation of host proteins. Our results indicate the presence of a novel mechanism mediating a fine balance between defence and counter-defence in which a SIM site is competitively sought for degradation and as a counter defense, {beta}C1 undergoes SUMOylation to escape from its degradation. Summary Statement{beta}C1 viral protein has evolved counter-defensive strategies to perturb host protein degradation pathways