Ectopic expression of an orchid (Oncidium Gower Ramsey) AGL6-like gene promotes flowering by activating flowering time genes in Arabidopsis thaliana

An AP1/AGL9 group of MADS box gene, OMADS1, with extensive homology to the Arabidopsis AGAMOUS-like 6 gene (AGL6) was characterized from orchid (Oncidium Gower Ramsey). OMADSI mRNA was detected in apical meristem and in the lip and carpel of flower. Yeast two-hybrid analysis indicated that OMADS1 is able to strongly interact with OMADS3, a TM6-like protein that was involved in flower formation and floral initiation in orchid. Transgenic Arabidopsis and tobacco ectopically expressed OMADS1 showed similar novel phenotypes by significantly reducing plant size, flowering extremely early, and losing inflorescence indeterminacy. In addition, homeotic conversion of sepals into carpel-like structures and petals into staminoid structures were also observed in flowers of 35S:: OMADSI Arabidopsis. This result indicated that OMADSI was involved in floral formation and initiation in transgenic plants. Further analysis indicated that the expression of flowering time genes FT, SUPPRESSOR OF OVEREX-PRESSION OF CO 1 (SOCI) and flower meristem identity genes LEAFY (LFY), APETALA1 (API) was significantly up-regulated in 355::OMADS1 transgenic Arabidopsis plants. Furthermore, ectopic expression of OMADSI rescued late-flowering phenotype in gi-1, co-3 but not for ft-1 and fwa-1 mutants. These results supported that ectopic expression of OMADSI influenced flower transition and formation by acting as an activator for FT and SOCI in Arabidopsis.