Effect of GA(3) Treatment on Seed Development and Seed-Related Gene Expression in Grape

BACKGROUND: The phytohormone gibberellic acid (GA(3)) is widely used in the table grape industry to induce seedlessness in seeded varieties. However, there is a paucity of information concerning the mechanisms by which GAs induce seedlessness in grapes. METHODOLOGY/PRINCIPAL FINDINGS: In an effort to systematically analyze the cause of this GA(3)-induced seed abortion, we conducted an in depth characterization of two seeded grape cultivars (‘Kyoho’ and ‘Red Globe’), along with a seedless cultivar (‘Thompson Seedless’), following treatment with GA(3). In a similar fashion to the seedless control, which exhibited GA(3)-induced abortion of the seeds 9 days after full bloom (DAF), both ‘Kyoho’ and ‘Red Globe’ seeded varieties exhibited complete abortion of the seeds 15 DAF when treated with GA(3). Morphological analyses indicated that while fertilization appeared to occur normally following GA(3) treatment, as well as in the untreated seedless control cultivar, seed growth eventually ceased. In addition, we found that GA(3) application had an effect on redox homeostasis, which could potentially cause cell damage and subsequent seed abortion. Furthermore, we carried out an analysis of antioxidant enzyme activities, as well as transcript levels from various genes believed to be involved in seed development, and found several differences between GA(3)-treated and untreated controls. CONCLUSION: Therefore, it seems that the mechanisms driving GA(3)-induced seedlessness are similar in both seeded and seedless cultivars, and that the observed abortion of seeds may result at least in part from a GA(3)-induced increase in cell damage caused by reactive oxygen species, a decrease in antioxidant enzymatic activities, and an alteration of the expression of genes related to seed development.