The co-expression of genes involved in seed coat and endosperm development promotes seed abortion in grapevine.

MAIN CONCLUSION: The seed coat gene VviAGL11 coordinates with endosperm development genes FIS2, PHERESE1 and IKU2 and functions as the key regulator in seed development and abortion processes in grapevine. Seed development is essential for the reproduction of flowering plants. Seed abortion is a specific characteristic that produces seedless berries and is often observed in cultivated grapevines. Although seedlessness is an important trait for table and dried grapevine production, the mechanism of seed abortion remains poorly understood. This research aimed to analyze the co-expression of the seed coat development gene VviAGL11 and the endosperm development genes FERTILIZATION INDEPENDENT SEED2 (FIS2), PHERESE1 and HAIKU2 (IKU2) that regulate seedless fruit development in grapevine. The transcript levels of VviAGL11, FIS2, PHERESE1 and IKU2 all decreased during seed abortion in the seedless grape 'Thompson Seedless' plants, compared to those of the seeded grape 'Pinot Noir'. The transcript levels of the salicylic acid (SA)-dependent defense response genes EDS1, NPR1, NDR1 and SID2 were higher in 'Thompson Seedless' than 'Pinot Noir' during seed development. Also, WRKY3, WRKY6 and WRKY52, which participate in the SA pathway, were higher expressed in 'Thompson Seedless' than in 'Pinot Noir', indicating that SA-dependent defense responses may regulate seed abortion. The genes related to synthesis and metabolism of gibberellic acid (GA) and abscisic acid (ABA) also showed differential expression between 'Thompson Seedless' and 'Pinot Noir'. Exogenous applications of plant growth regulators (PGRs) to inflorescences of three stenospermocarpy grapevines before flowering showed that GA3 was critical prominently in seed development. Therefore, the co-expression of seed coat and endosperm development-related genes, SA pathway genes, and genes for the synthesis and metabolism of GA3 together enhance seed abortion in seedless grapes.

New disease-resistant, seedless grapes are developed using embryo rescue and molecular markers.

Improving the operation of embryo rescue technology is a highly efficient way to breed new high-quality cultivars of seedless, disease-resistant grapes when using a stenospermocarpic Vitis vinifera L. (female parents) hybrid with Chinese wild Vitis (male parents). In this study, sampling time had a significant effect on embryo recovery. Four crosses were investigated to improve the embryo rescue efficiency by determining the best sampling time, which was found to be 40, 50, 55, and 57 days after pollination (DAP) for 'Flame seedless' × 'Ruby seedless', 'Kunxiang seedless' × 'Flame seedless', 'Ruby seedless' self-pollination and 'Ruby seedless' × 'Flame seedless', respectively. The highest percentage embryo germination ranged from 60.83 to 89.10% for four cross-combinations when the embryo was germinated on woody plant medium (WPM), with 1.0-µM thidiazuron (TDZ, a potent cytokinin). For 11 cross-combinations, the embryo recovery rate varied from 4.8 to 29.6% and the plant development rate varied from 17.1 to 78.9%. 'Ruby seedless' was the best female parent followed by 'Flame seedless'. The Grape Seedless gene Probe 1 (GSLP1) and SCF27 molecular markers were used to assist the identification of the seedless traits of the 388 progeny. A total of 309 plantlets were amplified, with the specific bands at 569-bp and 2k-bp being preliminarily considered as seedless. The S382-615 marker was used to identify the downy mildew resistance of the 'Ruby seedless' × 'Beichun' cross. Two F1 progeny were amplified, with the specific band at 615-bp being identified as downy mildew resistance.