Overexpression of tomatoSlBBX16andSlBBX17impacts fruit development and gibberellin metabolism

Abstract

AbstractBBXs are B-Box zinc finger proteins that can act as transcription factors and regulators of protein complexes. Several BBX proteins play important roles in plant development. TwoArabidopsis thalianamicroProteins belonging to the BBX family, named miP1a and miP1b, homotypically interact with and modulate the activity of other BBX proteins, including CONSTANS, which transcriptionally activates the florigen,FLOWERING LOCUS T. In tomato, the closest homologs of miP1a and miP1b are the microProteinsSlBBX16 andSlBBX17. To deepen our understanding of the role of tomato microProteins in flowering, we constitutively expressedSlBBX16/17 inArabidopsisand tomato and examined possible interacting partners. Overexpression of the two tomato microProteins inArabidopsiscaused a delay in the flowering transition; however, the effect was weaker than that observed inArabidopsisplants overexpressing the native miP1a/b. In tomato, overexpression ofSlBBX17prolonged the flowering period; this effect was accompanied by downregulation of the flowering inhibitorsSelf Pruning(SP) andSP5G.SlBBX16 andSlBBX17 are able to hetero-oligomerize with TCMP-2, a cystine-knot peptide involved in flowering pattern and fruit development in tomato. Increasing the expression of both tomato microProteins also caused alterations in fruit development: overexpression ofSlBBX17resulted in a diminished number and size of ripe fruits as compared to WT plants, while overexpression ofSlBBX16caused delayed fruit production up to the breaker stage. These effects were associated with changes in the expression of genes regulating gibberellin content.