Study on SlBBX16 and SlBBX17, two B-box microProteins implicated in tomato reproductive development, and their interacting partners

Plant microproteins (miPs) are peptides with a single protein-protein interaction domain. They can form inhibitory complexes by interacting homotypically with proteins containing identical domains or heterotypically through compatible domains. An example is the interaction between Arabidopsis miP1a/b with CONSTANS and TOPLESS. The resulting trimeric complex limits florigen induction. In tomato, the closest homologs of miP1a/b are BBX16 and BBX17, which interact heterotypically with the cystine-knot peptide TCMP-2. When TCMP-2 was overexpressed, anticipated flowering and early fruiting were observed. Overexpression of SlBBX16 did not affect flowering, while SlBBX17 overexpression prolonged flowering. The increased expression of both BBXs altered fruit development: in the case of SlBBX17, reduced ripe fruit production was observed, while for SlBBX16, an altered fruit set and delayed early growth. These effects were associated with changes in the expression of GA-responsive genes. To deepen the role of SlBBX16/17, we overexpress FLAG-tagged proteins. Co-IP analyses coupled to mass spectrometry are underway to identify whether these BBXs could form a multi-protein complex, likely with TCMP-2.