The arrest of development of abortive reproductive organs in the unisexual flower of Vitis vinifera ssp. silvestris

Abstract

During the first stages of development, flowers of most dioecious species are hermaphroditic, with their transition to unisexual flowers being the result of the developmental arrest of one set of reproductive organs. In this work, we describe the development of male and female flowers of the dioecious wild grape species Vitis vinifera ssp. silvestris through scanning electron microscopy analysis and cytological observations, focusing our attention on the transition from bisexual to unisexual development. We divide floral development of the wild grape into eight stages. Differences between male and female flowers appear first at stage 6, when the style and stigma start to differentiate in female but not in male flowers. Cytological analysis of the slowly growing abortive pistil of male flowers shows that megagametophyte formation is, surprisingly, not inhibited. Instead of pistil abortion in the male flower, sexual determination is accomplished through programmed death of external nucellus cells and some layers of integumentary cells. Sterility of male structures in female flowers follows a different pattern, with microspore abnormalities evident from the time of their release from the tetrad. Sterile microspores and pollen grains in female flowers display an abnormal round shape, lacking colpi and possessing uniformly thickened cell walls that impede germination.

The genetic basis of sex determination in grapevines (Vitis spp.)

“…Next, we observed a dense range of F-linked polymorphisms that distinguished F from H and M haplotypes (Fig. 3f) and could account for male sterility in females flowers, which includes reflexed filaments, lack of fertile pollen and pollen dimorphism (Caporali et al, 2003;Gallardo et al, 2009). Like Ramos et al (2014), we propose that females arose via hermaphroditic selfing.…”

“…Together, these results strongly support that an 8 bp deletion in INP1 in homozygous state causes male sterility. The nonsense mutation might be thus responsible for the absence of colpi in Vv sylvestris female pollen grains (Caporali et al, 2003;Gallardo et al, 2009). Abnormal pollen aperture formation has been also associated with parthenocarpy, the production of fruit without fertilization (Alva et al, 2015).…”

Portuguese wild grapevine genome re-sequencing (Vitis vinifera sylvestris)

“…One of the plants show male characteristics (WM), with no functional carpel and the other exhibits female 5 flowers (WF) with a complete carpel, but with reflexed stamens producing infertile pollen. Both of these individuals had almost the same number of SNPs identified (6,197,145 for WF and 6,575,026 for WM individual), and shared half of the occurrences (3,643,713 SNPs; Figure 2a).…”

“…One of the plants show male characteristics (WM), with no functional carpel and the other exhibits female 5 flowers (WF) with a complete carpel, but with reflexed stamens producing infertile pollen. Both of these individuals had almost the same number of SNPs identified (6,197,145 for WF and 6,575,026 for WM individual), and shared half of the occurrences (3,643,713 SNPs; Figure 2a). The InDels analysis showed the same tendency as the previous results: the number of occurrences in both individuals were similar (1,151,997 for WF and 1,177,918 events for WM) and about half of them were shared (637,320 events; Figure 2b).…”

Outcrossing potential between 11 important genetically modified crops and the Chilean vascular flora

“…Grapevines are of a clonal nature due to vegetative propagation, and the eventual use of seeds (mostly in breeding programs) presents problems associated with low germination due to a very tough seed coat. Vitis vinifera is principally wind pollinated (Huglin, 1998) and different flower types are described between wild (dioecious) and cultivated (hermaphroditic) vines (Caporali et al, 2003). Recent work determining parentage and paternitybased estimation using nuclear single sequence repeats determined that both wild-type species and cultivars influence each other either in open landscapes (depending on the distance between individuals) or in closed environments (Di Vecchi-Staraz et al, 2009).…”