THE PLANT CELL, Vol 6, Issue 6 777-787, Copyright © 1994 by American Society of Plant Biologists
A Model for Seed Transmission of a Plant Virus: Genetic and Structural Analyses of Pea Embryo Invasion by Pea Seed-Borne Mosaic Virus
D. Wang and A. J. Maule
Department of Virus Research, John Innes Institute, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom
Pea seed-borne mosaic virus (PSbMV), a seed-transmitted virus in pea and
other legumes, invades pea embryos early in development. This process is
controlled by maternal genes and, in a cultivar that shows no seed
transmission, is prevented through the action of multiple host genes
segregating as quantitative trait loci. These genes control the ability of
PSbMV to spread into and/or multiply in the nonvascular testa tissues,
thereby preventing the virus from crossing the boundary between the
maternal and progeny tissues. Immunocytochemical and in situ hybridization
studies suggested that the virus uses the embryonic suspensor 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 the inverse relationship
between the age of the mother plant for virus infection and the extent of
virus seed transmission.