Contrasting patterns in the spread of two seed-borne viruses in pea embryos.
Temporal and spatial patterns of pea seed-borne mosaic potyvirus (PSbMV) and pea early-browning tobravirus (PEBV) accumulation in embryos of Pisum sativum were analysed using in-situ hybridization and immunohistochemistry. The distribution of PSbMV, which infects embryos after fertilization, changed as the embryo developed and some tissues remained free of infection. In contrast, embryos were uniformly infected with PEBV from the earliest stages of embryo development, and PEBV was detected in the egg cell and pollen grains, indicative of gametic transmission. These observations suggest that gametically transmitted viruses may be appropriate as potential vectors for the ectopic and uniform expression of novel genes in embryonic tissues. Functional complementarity in the 2 processes of embryo invasion was investigated following co-inoculation with PSbMV and PEBV. Interference in PSbMV seed transmission by PEBV was observed but PEBV seed transmission remained unaffected by PSbMV.