Malvastrum Yellow Vein Virus Pathogenic Mechanisms

Geminiviruses are characterized by their geminate virion particles and circular single-stranded DNA (ssDNA) genome. Geminiviruses infect both monocols and dicots and have caused significant losses in many economically important crops. In China, several kinds of begomoviruses were identified in tomato, tobacco, squash, ageratum and malvaslrum in Yunnan, Guangxi and Hainan provinces.Virus sample Y200 showing yellow vein symptom was collected form Malvastrwn coromandelianum in Yuanmou of Yunnan province. Partial DNA-A sequence of Y200 is most closely related to that of Malvastrwn yellow vein virus (MYVV) DNA-A with 96.1% sequence identity. DNAP molecule was amplified from Y200 with specific primers for DNAp, Y200 DNAp. contains 1348 nucleotides, it has 96.1% nucleotide sequence identity with MYVV DNAp. The partial DNA-A and complete DNAP sequences conform that Y200 is an isolate of MYVV.In order to investigate the role of MYVV DNA-A and DNAp in pathogenecity, infectious clones of DNA-A and DNAp of MYVV isolate Y47 (MYVV-Y47) were constructed. Infectivity assay show that MYVV-Y47 DNA-A alone could systemically infect Nicoliana benthamiana, N. glulinosa and Petunia hybrida plants without symptoms MYVV-Y47 DNAp is required for the induction of the typical symptoms including yellow cein, severe leaf curling, in these host plants. Southern blot analysis show that MYVV DNAp depends on the helper viruses for their replication and, in turn, is required for helper virus accumulation. Thus, MYVVDNA-A and DNAp are mutually dependent.