A MODEL FOR SEED TRANSMISSION OF A PLANT-VIRUS - GENETIC AND STRUCTURAL-ANALYSES OF PEA EMBRYO INVASION BY PEA SEED-BORNE MOSAIC-VIRUS

Pea seed-borne mosaic virus (PSbMV), a seed-transmitted virus in pea a nd other legumes, invades pea embryos early in development. this proce ss is controlled by maternal genes and, in a cultivar that shows no se ed transmission, is prevented through the action of multiple host gene s segregating as quantitative trait loci. These genes control the abil ity of PSbMV to spread into and/or multiply in the nonvascular tests t issues, thereby preventing the virus from crossing the boundary betwee n the maternal and progeny tissues. Immunocytochemical and in situ hyb ridization studies suggested that the virus uses the embryonic suspens or as the route for the direct invasion of the embryo. The programmed degeneration of the suspensor during embryo development may provide a transient window for embryo invasion by the virus and could explain th e inverse relationship between the age of the mother plant for virus i nfection and the extent of virus seed transmission.