Fruit set is the earliest phase of fruit growth and represents the onset of ovary growth after successful fertilization. In parthenocarpy, fruit formation is less affected by environmental factors because it occurs in the absence of pollination and fertilization, making parthenocarpy a highly desired agronomic trait. Elucidating the genetic program controlling parthenocarpy, and more generally fruit set, may have important implications in agriculture, considering the need for crops to be adaptable to climate changes. Several phytohormones play an important role in the transition from flower to fruit. Further complexity emerges from functional analysis of floral homeotic genes. Some homeotic MADS-box genes are implicated in fruit growth and development, displaying an expression pattern commonly observed for ovary growth repressors. Here, we provide an overview of recent discoveries on the molecular regulatory gene network underlying fruit set in tomato, the model organism for fleshy fruit development due to the many genetic and genomic resources available. We describe how the genetic modification of components of this network can cause parthenocarpy, discussing the contribution of hormonal signals and MADS-box transcription factors.
Flowering and fruiting are processes subject to complex control by environmental and endogenous signals. Endogenous signals comprise, besides classical phytohormones, also signaling peptides and miniproteins. Tomato cystine‐knot miniproteins (TCMPs), which belong to a Solanaceous‐specific group of Cys‐rich protein family, have been recently involved in fruit development. TCMP‐1 and TCMP‐2 display a highly modulated expression pattern during flower and fruit development. A previous study reported that a change in the ratio of the two TCMPs affects the timing of fruit production. In this work, to investigate TCMP‐2 mode of action, we searched for its interacting partners. One of the interactors identified by a yeast two hybrid screen, was the B‐box domain‐containing protein 16 (SlBBX16), whose closest homolog is the Arabidopsis microProtein 1b implicated in flowering time control. We demonstrated the possibility for the two proteins to interact in vivo in tobacco epidermal cells. Arabidopsis plants ectopically overexpressing the TCMP‐2 exhibited an increased level of FLOWERING LOCUS T (FT) mRNA and anticipated flowering. Similarly, in previously generated transgenic tomato plants with increased TCMP‐2 expression in flower buds, we observed an augmented expression of SINGLE‐FLOWER TRUSS gene, the tomato ortholog of FT, whereas the expression of the antiflorigen SELF‐PRUNING was unchanged. Consistently, these transgenic plants showed alterations in the flowering pattern, with an accelerated termination of the sympodial units. Overall, our study reveals a novel function for TCMP‐2 as regulatory factor that might integrate, thanks to its capacity to interact with SlBBX16, into the signaling pathways that control flowering, and converge toward florigen regulation.
RNA interference (RNAi) is a post-translational regulatory mechanism that controls gene expression in plants. This process can be artificially induced by double-stranded RNA (dsRNA) molecules with sequence homology to target...
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