Evidence that the alpha a gene of barley stripe mosaic virus encodes determinants of pathogenicity to oat (Avena sativa).

Complementary DNA clones from which infectious RNA can be transcribed were used to map the genetic determinants for oat (Avena sativa L.) pathogenicity of barley stripe mosaic virus (BSMV). Pseudorecombinant analysis of BSMV strains ND18 (nonpathogenic to oat) and CV42 (pathogenic to oat) indicated that the ability to systemically infect oat mapped to RNA alpha. A homologous recombinant of ND18 (18 alpha TKTKIN), possessing nucleotides 2218 to 2454 from CV42 RNA alpha, induced symptoms on oat similar to those generated by wild-type CV42. Six amino acids encoded by the alpha a gene differ between ND18 (PQSQTK) and CV42 (TKTKIN) in this region. Fine structure recombinants that encoded subsets of the six amino acid changes either were slow in their infection phenotype (18 alpha TKTK and 18 alpha TQSQIN) relative to recombinant 18 alpha TKTKIN or were not infectious (18 alpha KTKIN and 18 alpha KTK) to inoculated oat plants. Neither coat protein antigen nor viral RNA was detected in inoculated plants that did not display symptoms. All recombinants infected isolated oat protoplasts, however, as determined by Northern and Western blots of extracts from inoculated oat protoplasts. The accumulation of viral genomic RNAs in protoplasts among the recombinants tested was similar, except for that of recombinant 18 alpha TKTK which was reduced by 30%. The data support an earlier suggestion (Y. Zheng, and M. C. Edwards, 1990, J. Gen. Virol. 71, 1865-1868) that resistance of oat to BSMV strain ND18 is due to restricted virus movement in planta and provide evidence that the alpha a protein itself may be involved in the movement of BSMV in the infected plant.