RICE FLOWERING LOCUS T 1 (RFT1/FT-L3) is the closest homologue of Heading date 3a (Hd3a), which is thought to encode a mobile flowering signal and promote floral transition under short-day (SD) conditions. RFT1 is located only 11.5 kb from Hd3a on chromosome 6. Although RFT1 RNAi plants flowered normally, double RFT1-Hd3a RNAi plants did not flower up to 300 days after sowing (DAS), indicating that Hd3a and RFT1 are essential for flowering in rice. RFT1 expression was very low in wild-type plants, but there was a marked increase in RFT1 expression by 70 DAS in Hd3a RNAi plants, which flowered 90 DAS. H3K9 acetylation around the transcription initiation site of the RFT1 locus had increased by 70 DAS but not at 35 DAS. In the absence of Hd3a and RFT1 expression, transcription of OsMADS14 and OsMADS15, two rice orthologues of Arabidopsis APETALA1, was strongly reduced, suggesting that they act downstream of Hd3a and RFT1. These results indicate that Hd3a and RFT1 act as floral activators under SD conditions, and that RFT1 expression is partly regulated by chromatin modification.
RFT1/FT-L3是Hd3a最近的同源基因，Hd3a编码一个可移动的开花信号，并促进短日照条件下的开花转换。RFT1位于6号染色体上，离Hd3a仅11.5 kb的距离。尽管RFT1-RNAi植株开花正常，但是RFT1-Hd3a双RNAi植株在播种后(DAS)多达300天时仍不开花，这表明Hd3a和RFT1是水稻开花必需基因。RFT1在野生型植株中表达非常低，但是在Hd3a-RNAi植株中，70 DAS时RFT1表达显著增加，而Hd3a-RNAi植株在90 DAS时开花。70 DAS时，RFT1转录起始位点附近的H3K9乙酰化明显增加，而35 DAS时没有明显变化。Hd3a和RFT1表达缺失时，与拟南芥APETALA1同源的的两个水稻基因OsMADS14和OsMADS15的转录显著降低，这表明它们可能作用于Hd3a和RFT1的下游。这些结果表明，Hd3a和RFT1是短日照条件下开花的激活因子，RFT1表达部分受到染色质修饰的调控。