Early embryo invasion as a determinant in pea of the seed transmission of pea seed-borne mosaic virus

Abstract

Seed transmission of an isolate of pea seed-borne mosaic virus (PSbMV) in several pea genotypes has been studied. Cross-pollination experiments showed that pollen transmission of PSbMV did not occur and accordingly, virus was not detected in pollen grains by ELISA or electron microscopy. Comparative studies between two pea cultivars, one with a high incidence of seed transmission and one with none, showed that PSbMV infected the floral tissues (sepals, petals, anther and carpel) of both cultivars, but was not detected in ovules prior to fertilization. Virus was detected equally well in seed coats of the progeny in both cultivars. Analysis of virus incidence and concentration in pea seeds of different developmental stages demonstrated that in the cultivar with a high incidence of seed transmission, PSbMV directly invaded immature embryos, multiplied in the embryonic tissues and persisted during seed maturation. In contrast, the cultivar without seed transmission did not show invasion of immature embryos by the virus; there was no evidence for virus multiplication or persistence during embryo development and seed maturation. Hence seed transmission of PSbMV resulted from direct invasion of immature pea embryos by the virus and the block to seed transmission in the nonpermissive cultivar probably occurred at this step.

Narrow Bottlenecks Affect Pea Seedborne Mosaic Virus Populations during Vertical Seed Transmission but not during Leaf Colonization

“…Because pathogens must cross several barriers intended to protect the developing embryo, the occurrence of narrow population bottlenecks during pathogen vertical transmission could be a quite general rule. The capacity of viruses to invade plant embryos and withstand seed maturation and desiccation depends both on virus and host genotypes, as demonstrated for PSbMV [23], [27], [39]. Seed transmission of PSbMV in pea occurs exclusively by direct invasion of immature embryos from virus-infected maternal tissues.…”

“…Such conditions are therefore favorable to the occurrence of strong virus population bottlenecks. Early infection of the mother plant is necessary for PSbMV vertical transmission to occur [23]. PSbMV invasion of pea embryos occurs from virus infection spreading from the maternal cells in the micropylar region of the embryo to the endosperm cytoplasm, then to the embryonic suspensor and finally to the embryo.…”

“…No pollen transmission of PSbMV was observed in this genotype [23]. Plants were grown under greenhouse conditions from November 2011 to April 2012.…”

Seed transmission of Sweet potato leaf curl virus in sweet potato (Ipomoea batatas)

“…The seeds produced from SPLCV‐infected floral tissues clearly tested positive for SPLCV. According to previous studies concerning seed transmission of viruses such as Apple latent spherical virus , PSbMV and Cucumber mosaic viru s (CMV), the invasion route of virus to seed (especially invasion to embryo) was the most important determinant of seed transmission (Wang & Maule, ; Yang et al ., ; Nakamura et al ., ). In the present study, PCR tests showed that SPLCV was located inside the seed, indicating that SPLCV can be a seedborne virus and can be transmitted from seeds to a next‐generation plant via the embryo.…”

Multiple viral determinants affect seed transmission of pea seedborne mosaic virus in Pisum sativum

“…This suggests that several virus-host factor interactions determine the spread and accumulation of PSbMV in the maternal testa tissue. Whereas PSbMV can enter the embryo after fertilization (Wang & Maule, 1992), seed transmission of BSMV depends mainly on the ability of the virus to reach the reproductive tissues prior to fertilization (Edwards, 1995). Despite this difference, replication and movement also play central roles in seed transmission of BSMV, the major determinants being the RNA~ 5' UTR, a 369 repeat in the 7a gene, and the 7b gene.…”