Mapping of the Seed Transmission Determinants of Barley Stripe Mosaic Virus. Michael C. Edwards . Agricultural Research Service, United States Department of Agriculture, Northern Crop Science Laboratory, Fargo, ND 58105-5677 U.S.A. . MPMI 8:906-915. Accepted 10 July 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995.

The specific mechanism(s) by which some plant viruses are transmitted through seed, while others are excluded, is not known. Using infectious barley stripe mosaic virus (BSMV) RNAs transcribed in vitro from full-length cDNA clones, the viral genetic determinants of seed transmission have been mapped. Both pseudorecombinant and chimeric viruses were constructed from BSMV strains ND18 (seed transmitted) and CV17 (not seed transmitted). The markedly different seed transmissibility of these two strains facilitated the identification of RNA( as the location of the primary determinants of seed transmission phenotype. RNA( also played a role in seed transmission, but to a lesser extent than RNA(. Major genetic determinants of seed transmission on RNA( included the 5' untranslated leader, a 369-nt repeat in the (a gene, and the (b gene. Important determinants of symptom phenotype mapped to the RNA( leader and the (b gene as well. Some heterolo-gous combinations of the RNA( leader and the (b gene resulted in dramatic changes in symptomatology and seed transmission, depending on the parental source of RNAs( and (. These results suggest that a complex interaction of the RNA( leader, the (b gene, and RNAs( and ( are involved in BSMV pathogenesis. Considering the putative regulatory role of the (b gene (Donald and Jackson 1994, Plant Cell 6:1593-1606) and the trans effects that alterations in the ? b gene have on RNA? gene expression (Petty et al., 1990, EMBO J. 9:3453-3457), phenotypic effects attributed to elements of RNA? could result from cis or trans interactions involving the RNA( leader, the (b gene, and RNAs ( and ( Clearly, virus replication and movement play pivotal roles in the seed transmission of BSMV.