Contrasting patterns in the spread of two seed-borne viruses in pea embryos

The temporal and spatial patterns of pea seed-borne mosaic potyvirus (PSbMV) and pea early browning tobravirus (PEBV) accumulation in pea embryos were analyzed using in-situ hybridization and immunohistochemistry. For PSbMV, which infects embryos after fertilization, the distribution changed as the embryo developed and some tissues remained free of virus 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 into the embryo. 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 two processes of embryo invasion was tested following co-inoculation with PSbMV and PEBV. Instead of complementation, interference in PSbMV seed transmission by PEBV was observed; PEBV seed transmission remained unaffected by PSbMV.