Genes that influence yield in tomato

Abstract

Yield is the most important breeding trait of crops. For fruit-bearing plants such as Solanum lycopersicum (tomato), fruit formation directly affects yield. The final fruit size depends on the number and volume of cell layers in the pericarp of the fruit, which is determined by the degree of cell division and expansion in the fertilized ovaries. Thus, fruit yield in tomato is predominantly determined by the efficiency of fruit set and the final cell number and size of the fruits. Through domestication, tomato fruit yield has been markedly increased as a result of mutations associated with fruit size and genetic studies have identified the genes that influence the cell cycle, carpel number and fruit set. Additionally, several lines of evidence have demonstrated that plant hormones control fruit set and size through the delicate regulation of genes that trigger physiological responses associated with fruit expansion. In this review, we introduce the key genes involved in tomato breeding and describe how they affect the physiological processes that contribute to tomato yield.

Keywords: fruit size; parthenocarpy; plant hormones; tomato; yield.

Fig. 1

Model for fruit set initiation and development. The carpel arises from the meristem (phase I). Upon pollination and fertilization, auxin and gibberellin (GA) synthesis are stimulated in the ovary. Auxin induces fruit growth by activating cell division and stimulating fruit set initiation (phase II), whereas GA induces fruit growth by activating cell expansion (phase III). Abscisic acid (ABA) and cytokinin (CK) may antagonize auxin or GA action to suppress fruit set initiation before anthesis, while CK may induce cell division after anthesis. ABA may act in phase III to stimulate fruit expansion.

Fig. 2

Schematic model for the regulation of parthenocarpic fruit formation by the components of hormonal signaling pathways. Parthenocarpy is induced by the action of several components involved in the signaling pathway of various hormones, especially ethylene, auxin, gibberellin and cytokinin. SlTPR1 and SlTIR1 could act as positive regulators of fruit set initiation, while AUCSIA, SlARF7, SlIAA9, SlDELLA and SlCHS could act as negative regulators of fruit set initiation. Three pat mutations, pat, pat2 and pat3/pat4, may be associated with GA synthesis or signaling. AUCSIA: auxin cum silencing action, SlARF7: Solanum lycopersicum auxin response factor 7, SlCHS: Solanum lycopersicum chalcone synthase, SlDELLA: Solanum lycopersicum DELLA, SlTIR1: Solanum lycopersicum transport inhibitor response protein 1, SlTPR1: Solanum lycopersicum tetratricopeptide repeat protein 1.