Falsiflora and anantha control early stages of floral meristem development in tomato (Lycopersicon esculentum Mill.)

Abstract

The shoot apical meristem of tomato gives rise to a relatively fixed number of vegetative nodes before converting to an inflorescence meristem. Growth of the plant after inflorescence initiation is continued by a sympodial bud in the axil of the last-formed leaf. We show that the inflorescence meristem produces flower meristems not as lateral primordia, but by a series of nearly equal divisions, each time yielding a flower meristem and an inflorescence meristem. We describe two mutants, falsiflora and anantha, that block the acquisition of floral meristem identity by the products of the inflorescence meristem. In both mutants the vegetative meristem successfully converts to an inflorescence meristem (although this is delayed in falsiflora), and the inflorescence meristem functions morphologically the same as in the wild type. But determinate flower meristems are replaced by indeterminate proliferous shoots with a combination of inflorescence and vegetative characters. The falsiflora inflorescence is very leafy with substantial internode elongation and may easily reach a meter in length. The anantha inflorescence is reminiscent of the common cauliflower variant of Brassica (B. oleracea var. botrytis). Leaves within the anantha inflorescence, although still present, are highly suppressed. Normal flowers never form, but occasionally some aberrant floral structures may be found in very large anantha inflorescences. Based on phenotypic comparison, falsiflora appears to be blocked at an earlier stage than is anantha. Consistent with this, falsiflora is completely epistatic to anantha. We discuss our findings in the context of characterized meristem identity mutants in other species, and of partial flowering experiments indicating that the vegetative to floral transition is, at least in many species, a series of small steps rather than an all or none transformation.