Molecular characterization of two highly divergent Iranian johnsongrass mosaic virus isolates from Zea mays

Iranian johnsongrass mosaic virus (IJMV, genus Potyvirus, family Potyviridae) is one of the most prevalent viruses causing maize mosaic disease in Iran. In this study, the complete genomes (9,618 and 9,543 nucleotides) of two highly divergent IJMV isolates (Maz2 and Maz3) were obtained from the metagenomic analysis of Zea mays RNAs using Illumina sequencing. The genome contained a single open reading frame (9,165 nucleotides) encoding a polyprotein of 3,054 amino acids, flanked by a 5'-untranslated region (UTR) of 216 and 143 nucleotides and a 3'-UTR of 237 and 235 nucleotides. A comparative analysis of the complete genome showed that IJMV-Maz2 and Maz3 had 85.99% nucleotide and 94.56% amino acid sequence identity with each other and shared 84.87-88.74% nt and 94.24-96.17% aa identity with those of two other IJMV isolates available in the GenBank. The coat protein of Maz2 and Maz3 showed 86.40-95.72% nt sequence identity (90.79-97.70% aa identity) to 12 other IJMV isolates available in GenBank. Our results indicated a relatively stable and conserved genomic composition with a low codon usage bias in all of the assayed IJMV coding sequences. Analysis of various population genetics parameters and distribution of synonymous and nonsynonymous mutations revealed that purifying selection pressure was the major force acting upon the IJMV genome. The outcome of the study provides valuable insights on the evolution of IJMV genome, for which there are few genome sequences available, and informs the current breeding efforts towards resistance for IJMV.