THE SELF-PRUNING GENE OF TOMATO REGULATES VEGETATIVE TO REPRODUCTIVE SWITCHING OF SYMPODIAL MERISTEMS AND IS THE ORTHOLOG OF CEN AND TFL1

Vegetative and reproductive phases alternate regularly during sympodia l growth in tomato. In wild-type 'indeterminate' plants, inflorescence s are separated by three vegetative nodes. In 'determinate' plants hom ozygous for the recessive allele of the SELF-PRUNING (SP) gene, sympod ial segments develop progressively fewer nodes until the shoot is term inated by two consecutive inflorescences. We show here that the SP gen e is the tomato ortholog of CENTRORADIALIS and TERMINAL FLOWER1, genes which maintain the indeterminate state of inflorescence meristems in Antirrhinum and Arabidopsis respectively: The sp mutation results in a single amino acid change (P76L), and the mutant phenotype is mimicked by overexpressing the SP antisense RNA. Ectopic and overexpression of the SP and CEN transgenes in tomato rescues the 'indeterminate' pheno type, conditions the replacement of flowers by leaves in the infloresc ence and suppresses the transition of the vegetative apex to a reprodu ctive shoot. The SELF-PRUNING gene is expressed in shoot apices and le aves from very early stages, and later in inflorescence and floral pri mordia as well. This expression pattern is similar to that displayed b y the tomato ortholog LEAFY and FLORICAULA. Comparison of the sympodia l, day-neutral shoot system of tomato and the monopodial, photoperiod- sensitive systems of Arabinopsis and Antirrhinum suggests that floweri ng genes that are required for the processing of floral induction sign als in Arabidopsis and Antirrhinum are required in tomato to regulate the alternation between vegetative and reproductive cycles in sympodia l meristems.