The interplay between GA (gibberellin) and AGE (miR156 node) pathways controlling tomato flowering

Abstract

The transition of the shoot apical meristem from vegetative to reproductive produces molecular, morphological and physiological changes, impacting the entire plant body. This process, which is influenced by environmental cues, genetic control and hormonal regulation is termed flowering. Arabidopsis thaliana, a well-known model for studying flowering control has five different pathways contributing for this complex and important developmental process. Among these five pathways, autonomous, vernalization and photoperiod do not play fundamental roles in species like tomato (Solanum lycopersicum L.). In this way, the other two flowering routes known as GA (controlled by the phytohormone gibberellin) and AGE (controlled by the miR156/SQUAMOSA PROMOTOR BINDING LIKE (SPL) pathway) should play bigger roles controlling the phase change in this late species. Recently, it was demonstrated physical protein-protein interactions between SPL (direct targets of miR156) and DELLA (negative regulator of GA response) orchestrating the interplay between these two pathways in Arabidopsis. Interestingly, while GA promotes flowering in Arabidopsis in long day conditions, it represses flowering in tomato. To understand the genetic interactions between both pathways in tomato, we produced double transgenic-mutants affecting the level of the miR156 coupled with three different mutations associated with GA. In all three mutants, overexpression of miR156 results in highly delaying in flowering time, suggesting genetic interaction among GA and AGE pathways in tomato. It is possible that tomato DELLA and SPLs interact physically as in Arabidopsis. We propose that this protein-protein interaction includes the miR156 binding site sequence, which is found in some SPLs. In this proposal, we intend to evaluate the patterns of interaction between the unique DELLA in tomato (PROCERA) and three different SPLs by using yeast two hybrid and BiFC (Bimolecular fluorescent complement assay). The conservation of this molecular interaction in tomato and Arabidopsis would indicate that GA-repressed and GA-induced flowering species, respectively, use common genetic pathways with opposite developmental outputs. (AU)