Investigation of the role of B-box MicroProteins in the tomato reproductive development

Microproteins (miPs) are single-domain proteins that act as post-translational regulators of protein complexes. A central role of two Arabidopsis miPs, miP1a and miP1b, in the control of flowering time has recently been identified. These miP1s are members of the BBX family, a group of zinc-finger transcription factors and regulators. BBX proteins are characterised by a B-Box motif, responsible for protein-protein interaction. It has been shown that both miP1a and miP1b actively participate in the Arabidopsis flowering process by mediating the recruitment of CONSTANS (CO) into a repressor complex with TOPLESS (TPL). In Arabidopsis, the interaction of CO with miP1a/b and TPL causes a reduction in the expression of FLOWERING LOCUS T resulting in a delay in flowering. SlBBX16 and SlBBX17 are the tomato homologs of miP1b and miP1a, respectively. As there is no evidence in the literature for the presence in tomato of a flowering inhibitor complex similar to that in Arabidopsis, we checked the interactions between SlBBX16/17 with key flowering regulators by yeast-two-hybrid analysis. We also monitored the reproductive phenotypes of Arabidopsis and tomato plants overexpressing SlBBX16/17.