FA controls floral meristem identity
FA is required for initiation of the developmental programme that produces flowers in the apical meristem of tomato. The conversion of flowers into indeterminate shoots in the fa inflorescence indicates that FA is a key gene in the control of floral meristem identity. The same function has been demonstrated for FLO/LFY genes in Antirrhinum ( Coen et al. 1990 ), Arabidopsis ( Weigel et al. 1992 ), Petunia ( Soueret al. 1998 ) and pea ( Hofer et al. 1997 ) on the basis of their loss-of-function mutants. Moreover, ectopic branches in these mutants develop vegetative structures such as cauline leaves or bracts. In tomato fa mutant, the transformed meristem also acquires the developmental programme of a vegetative meristem. All primary and higher-order shoots of the inflorescence produce leaves and are able to reach a regular sympodial transition. Pnueli et al. (1998) suggested that the tomato scorpioid inflorescence can be interpreted as a vegetative shoot in which leaf development is suppressed and each flower constitutes a modified sympodial with one internode instead of three. This interpretation explains not only the ‘zig-zag’ phyllotaxis of the tomato inflorescence, but also the fa inflorescence development. In this sense, during tomato inflorescence development FA would regulate both the specification of the floral meristem identity, and the maintenance of the suppression of vegetative development and leaf formation. In this latter role, FA might act redundantly with other genes since leaves are initially suppressed in fa inflorescence branches.