SHORT INTEGUMENT (SIN1), A GENE REQUIRED FOR OVULE DEVELOPMENT IN ARABIDOPSIS, ALSO CONTROLS FLOWERING TIME

The short integument (sin1) mutation causes a female-specific infertil ity, and a defect in the control of time to flowering in Arabidopsis. Female sterility of Sin(-) plants is due to abnormal ovule integument development and aberrant differentiation of the megagametophyte in a s ubset of ovules. An additional defect of sin1 mutants is the productio n of an increased number of vegetative leaf and inflorescence primordi a leading to delayed flowering. The delayed flowering phenotype of sin 1-1 is not due to a defect in the perception of day length periodicity or in gibberellic acid metabolism. Phenotypes of double mutant combin ations of sin1 with terminal flower (tfl1) indicate that SIN1 activity is required for precocious floral induction typical in a tfl1 mutant. Unexpectedly, sin1-1 tfl1-1 plants do not make pollen, thus revealing a novel role for TFL1 in the anther. Early flowers of sin1-1 ap1-1 do uble mutants are transformed to long inflorescence-like shoots. A gene tic model for the role of SIN1 in flowering time control is proposed.