Transition to Flowering and Morphogenesis of Reproductive Structures in Tomato

Flowering in tomato (Solanum lycopersicum L.) has long been investigated by plant physiologists and horticulturists aiming to increase productivity of this important fruit crop. The disruption of the sequence of events which give rise to normal evelopment of the reproductive structures by either the manipulation of the environment, hormones or mutations has provided information useful to unravel the complexity of the implicated mechanisms. In this paper, we focus on the early stages of the flowering process, analysing how flowering time and reproductive morphogenesis are regulated. Development of the reproductive structures up to anthesis, having been reviewed on several occasions in the past, is not considered. Tomato is an autonomously flowering plant with a sympodial growth habit, which means that it flowers repeatedly, at the top of an initial segment and of successive sympodial segments. The nature of its reproductive structure, a raceme or a cyme, is still questioned but available evidence supports the view that the tomato inflorescence is racemose. Flowering time is strongly dependent on the daily light energy integral and is regulated by an array of genes among which SINGLE FLOWER TRUSS (SFT) and SELF PRUNING (SP) play a major role. SFT is a flowering promoter particularly active in the initial segment while SP regulates sympodial development by controlling the regularity of the vegetative-reproductive switch of the different sympodial segments. Many genes specifying the identity of the meristems and floral organs interact to regulate the morphogenesis of the reproductive structures, opening a large field for future investigations.