Abstract
Mulberry crinkle leaf virus (MCLV) is a member of the genus Mulcrilevirus, family Geminiviridae. The expression and functions of the V4 and V5 genes encoded by the MCLV genome remain unknown. Here, we confirmed the expression of V4 and V5 by analyzing the V4 and V5 mRNAs and the promoter activity of individual ORFs upstream sequences. The functions of V4 and V5 were investigated by constructing Agrobacterium-mediated infectious clones of wild-type MCLV variant П (MCLV vII), MCLV(wt) and MCLV vП mutants, such as MCLV(mV4) (start codon of V4 ORF mutated), MCLV(dV4) (5'-end partial deletion of V4 ORF sequence) and MCLV(mV5) (V5 ORF start codon mutated). Although MCLV(wt), MCLV(mV4), and MCLV(dV4) could infect natural host mulberry and experimental tomato plants systematically, the replication of the MCLV(mV4) and MCLV(dV4) genomes was obviously reduced compared to MCLV(wt) in both mulberry and tomato plants. MCLV vП expressing V5 could infect Nicotiana benthamiana plants systematically, but MCLV(mV5) could not, implying that V5 is needed for MCLV vП to infect N. benthamiana plants. Taken together, V4 is involved in replication of the MCLV genome in host plants, and V5 potentially might extend the host range. Our findings lay a foundation for in-depth insight into the functions of MCLV-encoded proteins and provide a novel perspective for the subsequent study of MCLV-host plant interactions.