Involvement of the tomato BBX16 and BBX17 microProteins in reproductive development.

BBXs 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. Two Arabidopsis thaliana microProteins 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. Arabidopsis plants overexpressing miP1a and miP1b showed delayed flowering. In tomato, the closest homologs of miP1a and miP1b are the microProteins Sl BBX16 and Sl BBX17. This study was aimed at investigating whether the constitutive expression of Sl BBX16/17 in Arabidopsis and tomato impacted reproductive development. The heterologous expression of the two tomato microProteins in Arabidopsis caused a delay in the flowering transition; however, the effect was weaker than that observed when the native miP1a/b were overexpressed. In tomato, overexpression of SlBBX17 prolonged the flowering period; this effect was accompanied by downregulation of the flowering inhibitors Self Pruning (SP) and SP5G. Sl BBX16 and Sl BBX17 can hetero-oligomerize with TCMP-2, a cystine-knot peptide involved in flowering pattern regulation and early fruit development in tomato. The increased expression of both microProteins also caused alterations in tomato fruit development: we observed in the case of SlBBX17 a decrease in the number and size of ripe fruits as compared to WT plants, while for SlBBX16 , a delay in fruit production up to the breaker stage. These effects were associated with changes in the expression of GA-responsive genes. [Display omitted] • MicroProteins interact with and regulate the activity of large protein complexes. • Tomato BBX16 and BBX17 are microProteins belonging to B-Box family. • Sl BBX16 and Sl BBX17 interact with a tomato cystine-knot peptide. • Increasing expression of Sl BBX17 prolongs the flowering period. • Both Sl BBX16 and Sl BBX17 affect fruit development and GA metabolism. [ABSTRACT FROM AUTHOR]