Hd3a and RFT1 are essential for flowering in rice

Abstract

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.

Inflorescence Meristem Identity in Rice Is Specified by Overlapping Functions of Three AP1/FUL-Like MADS Box Genes and PAP2, a SEPALLATA MADS Box Gene

“…Although it has been suggested that MADS14 and MADS15 act downstream of Hd3a/RFT1 in the meristem, their functions in this pathway have not been clearly elucidated (Komiya et al, 2008(Komiya et al, , 2009Taoka et al, 2011). Misexpression of Hd3a causes extremely early flowering in rice and a number of other plant species (Izawa et al, 2002;Tamaki et al, 2007).…”

“…It has been proposed that MADS14 and MADS15 function downstream of Hd3a and RFT1 to transduce the florigen signal (Komiya et al, 2008(Komiya et al, , 2009). More recently, transient assays in cultured cells were used to show that the transcription of MADS15 is indeed induced by a complex containing Hd3a, a 14-3-3 protein, and FD (Taoka et al, 2011).…”

“…The IM starts to initiate inflorescence branch meristem (BM) primordia. Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) function as major components of florigen in rice (Tamaki et al, 2007;Komiya et al, 2008Komiya et al, , 2009. Recent findings show that Hd3a protein generated in leaves is transported to the cytoplasm of shoot apex cells where it interacts with 14-3-3 proteins (Taoka et al, 2011).…”

“…This implies that, in the meristem, FD and possibly other downstream targets of Hd3a and RFT1 induce genes that promote meristem phase transition. Expression of both MADS14 and MADS15, which encode AP1/FUL-like MADS domain proteins, was suppressed in Hd3a and RFT1 double knockdown plants, suggesting that these genes function downstream of the florigen signal (Komiya et al, 2008(Komiya et al, , 2009). Moreover, it has been demonstrated that MADS15 transcription is induced by phosphorylated FD in the presence of Hd3a (Taoka et al, 2011).…”

A Drought-Inducible Transcription Factor Delays Reproductive Timing in Rice

“…Rice is a facultative short-day plant that flowers earlier in short days (SDs) than in long days (LDs). Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) are two paralogous genes in rice encoding "florigen" molecules expressed in the phloem of leaves and transported to the shoot apical meristem to promote flowering (Tamaki et al, 2007;Komiya et al, 2008Komiya et al, , 2009Tsuji et al, 2013). Heading date 1 (Hd1, counterpart of Arabidopsis [Arabidopsis thaliana] CONSTANS, CO), Days to heading 2 (DTH2, encoding another CO-like protein), and Early heading date 1 (Ehd1) regulate expression of these two "florigen" genes.…”