Early flowering and increased expression of a FLOWERING LOCUS T-like gene in chrysanthemum transformed with a mutated ethylene receptor gene mDG-ERS1(etr1-4)

Ethylene has an inhibitory effect on flowering in a short-day (SD) plant chrysanthemum (Chrysanthemum morifolium Ramat.). In this study, we used a hexaploid chrysanthemum 'Sei-Marine' and found that its transgenic lines transformed with a mutated ethylene receptor gene mDG-ERS1(etr1-4), which conferred reduced ethylene sensitivity (J. Plant Biol. 51: 424-427, 2008), opened flowers earlier than the non-transformed control. We examined whether the accelerated flower induction in the transformant occurred through the enhanced expression of chrysanthemum genes homologous to FLOWERING LOCUS T (FT), a floral inducer gene in Arabidopsis. We cloned three cDNAs for FT homologs (CmFTL1, CmFTL2, and CmFTL3) from 'Sei-Marine'. CmFTL2 putatively encodes a non-functional gene product due to a frame shift caused by a 2 bp-deletion in the coding region. RT-PCR analysis revealed differential expression patterns of CmFTL genes in the transgenic and control lines, suggesting that these genes might be under the control of ethylene. CmFTL1/2 mRNA level was lower in a SD condition than a long-day (LD) condition. CmFTL3 mRNA accumulated abundantly under SD condition as compared with LD condition in the transgenic line. These results suggest the association of increased expression of CmFTL3 gene with the accelerated flowering in the transgenic line with reduced ethylene sensitivity.