DELLA proteins positively regulate seed size in Arabidopsis.

Human and animal nutrition is mainly based on seeds. Seed size is a key factor affecting seed yield and has thus been one of the primary objectives of plant breeders since the domestication of crop plants. Seed size is coordinately regulated by signals of maternal and zygotic tissues that control the growth of the seed coat, endosperm, and embryo. Here, we provide novel evidence of the role of DELLA proteins, key repressors of gibberellin responses, in the maternal control of seed size. The gain-of-function della mutant gai-1 produces larger seeds due to an increase in the cell number in ovule integuments. This leads to an increase in ovule size and, in turn, an increase in seed size. Moreover, DELLA activity promotes increased seed size by inducing the transcriptional activation of AINTEGUMENTA, a genetic factor that controls cell proliferation and organ growth, in the ovule integuments of gai-1. Overall, our results point to DELLA proteins as new players in control of seed size and suggest that modulation of the DELLA-dependent pathway could be used to improve crop yield.