Complete genomic characterization of a novel orfanplasmovirus from Alternaria alternata f. sp. mali.

Alternaria alternata orfanplasmovirus 1 (AaOrfV1), a previously unreported orfanplasmovirus, was discovered in strain TG155-3 of Alternaria alternata f. sp. mali in this study. The genome of AaOrfV1 consists of two positive-sense single-stranded RNA segments. RNA1, which is 3122 nucleotides in length, encodes a protein with 973 amino acids. BLASTp analysis showed that this protein had the highest sequence similarity (62.79% identity) to the RNA-dependent RNA polymerase of downy mildew lesion associated orfanplasmovirus 4. RNA2, with a length of 2,485 nucleotides, encodes a protein with 785 amino acids that showed the highest similarity (44.02% identity) to a hypothetical protein of downy mildew lesion associated orfanplasmovirus 7. Phylogenetic analysis indicated that AaOrfV1 clusters with other reported orfanplasmoviruses, supporting its classification as a new member of the proposed family "Orfanplasmoviridae". This is the first report of the complete genome sequence of an orfanplasmovirus from Alternaria alternata f. sp. mali. These findings significantly enhance our understanding of orfanplasmoviruses and the diversity of mycoviruses in A. alternata.