Functional divergence of the TFL1-like gene family in Arabidopsis revealedby characterization of a novel homologue

Background: The TERMINAL FLOWER 1 (TFL1) gene of Arabidopsis plays an impor tant role in regulating flowering time and in maintaining the fate of inflo rescence meristem (IM). TFL1 is a homologue of CENTRORADIALIS (CEN) from An tirrhinum, which is only involved in IM maintenance. Recent mutational stud ies and the genome project revealed that TFL1 belongs to a small gene famil y in Arabidopsis, in which functional divergence may have occurred among th e members. Results: We found a new member of the TFL1 gene family, which is mapped on chromosome 2 of Arabidopsis. The predicted protein sequence encoded by this gene is more closely related to that of CEN than other Arabidopsis TFL1 ho mologues (and therefore named ATC for Arabidopsis thaliana CENTRORADIALIS h omologue). Transgenic plants constitutively expressing the ATC gene (35S::A TC), in either wild-type or tfl1 mutant backgrounds, showed a phenotype sim ilar to that observed in transgenic plants constitutively expressing the TF L1 gene. However, in contrast to TFL1, the expression of ATC was only detec ted in the hypocotyl of young plants, and not in the IM. In addition, an at c loss-of-function mutant, isolated by screening a T-DNA library, showed no phenotypes that were similar to those of tfl1 mutants. Conclusion: The phenotypes of transgenic plants over-expressing ATC suggest that the ATC protein can functionally substitute for TFL1. However, the pa ttern and level of expression and the loss-of-function phenotype indicate t hat ATC does not participate in the regulation of IM identity, but rather h as a role that is different from that of TFL1.