Gibberellins negatively modulate ovule number in plants

Abstract

Ovule formation is a complex developmental process in plants with a strong impact on the production of seeds. Ovule primordia initiation is controlled by a gene network, including components of the signaling pathways of auxin, brassinosteroids and cytokinins. In contrast, gibberellins (GAs) and their signaling negative regulators DELLA proteins have never been shown to be involved in ovule initiation. Here we provide molecular and genetic evidences that point to DELLA proteins as novel players in the determination of ovule number in Arabidopsis and in species of agronomic interest like tomato and rapeseed, adding a new layer of complexity to this important developmental process. DELLA activity correlates positively with ovule number, acting as a positive factor for ovule initiation. In addition, ectopic expression of a dominant DELLA in the placenta is sufficient to increase ovule number. The role of DELLA proteins in ovule number seems not to be related to auxins transport or signaling in the ovule primordia. A possible crosstalk of DELLA proteins with the molecular and hormonal network controlling ovule initiation is discussed.