Complete Genome Sequence of a Chinese Isolate of Potato virus X and Analysis of Genetic Diversity

The complete genomic sequence of a Chinese Potato virus X isolate FX21 (PVX-FX21) was determined from three overlapping cDNA clones. The genome of PVX-FX21 is 6435 nucleotides in length excluding the poly(A) tail and contains five open reading frames (ORFs). Its entire genomic sequence shares 95.2– 96.3% identities with Asian and European isolates, and 77.3–77.8% with American isolates. Phylogenetic analysis of the complete genomic sequence reveals two groups: the Eurasian group and the American group. PVX-FX21 belongs to the Eurasian group and forms a separate sub-branch with three Asian isolates. Similar analyses of the coat protein genes of 37 PVX isolates also reveal two major groups. All PVX isolates from Asia are clustered to group I, whereas isolates from Europe and America are clustered to both groups. Nucleotide sequence diversity analyses show that there is no geographical differentiation between PVX isolates and that constraint on the ORF encoding RNA-dependent RNA polymerase is much higher than those on the other four ORFs.