Nucleotide sequences of apple stem pitting virus and of the coat protein gene of a similar virus from pear associated with vein yellows disease and their relationship with potex- and carlaviruses
The nucleotide sequence (9306 nucleotides) of cDNA clones of apple stem pitting virus (ASPV) obtained from a double-stranded RNA template, extracted from diseased plant tissue, was determined. The genome is composed of five open reading frames (ORFs) encoding putative proteins with M rs of 247083, 25147, 12832, 7429 and 43712, and has a poly(A) tail. Using two oligonucleotides designed from the ASPV sequence information a 1598 bp fragment from near the 3′ terminus of the viral RNA, containing the coat protein of M r 43766, was amplified from vein yellows (VY)-infected pear plants by PCR. The sequence determined showed eight nucleotide changes resulting in five amino acid substitutions compared with the sequence of ASPV. When compared to potex-, carla-, clostero- and capillo-viruses, the ASPV genome organization appeared to be most closely related to that of potexviruses, but with a larger coat protein of M r 44K (ORF5). The predicted coat protein size was confirmed by immunoblot analysis. The results show that ASPV does not fall into subgroup A of the closteroviruses but that it probably belongs in an as yet undefined group of viruses. They also suggest that the virus associated with VY is a strain of ASPV.