Analysis of Pathogenicity and Virulence Factors of Ageratum leaf curl Sichuan virus

Abstract

<i>Ageratum leaf curl Sichuan virus</i> (ALCScV) is a novel monopartite begomovirus, which was identified from <i>Ageratum conyzoides</i> plants in Sichuan Province, China. In this study, we showed that ALCScV can induce typical dwarf and downward leaf-curling symptoms in <i>Ageratum conyzoides</i>, <i>Helianthus annuus</i>, and <i>Nicotiana benthamiana</i> plants and that the noncognate betasatellite can enhance disease symptoms and increase viral accumulation. Expression of the ALCScV-encoded V2, C1, and C4 proteins through a <i>Potato virus X</i> (PVX) vector caused severe symptoms in <i>N. benthamiana</i>. Further study revealed no symptoms in <i>N. benthamiana</i> plants inoculated with infectious ALCScV clones lacking the C4 protein and that the relative viral DNA accumulation levels significantly decreased when compared with ALCScV-inoculated plants. Thus, our mutational analyses demonstrated that C4 is a pathogenicity determinant that plays key roles in symptom formation and virus accumulation. Furthermore, we also demonstrated that the second glycine of C4 was critical for ALCScV pathogenicity.