The florigen interactor BdES43 represses flowering in the model temperate grass Brachypodium distachyon

Abstract

FLOWERING LOCUS T (FT) protein, physiologically florigen, has been identified as a system integrator of numerous flowering time pathways in many studies, and its homologs are found throughout the plant lineage. It is important to uncover how precisely florigenic homologs contribute to flowering initiation and how these factors interact genetically. Here we dissected the function of Brachypodium FT orthologs BdFTL1 and BdFTL2 using overexpression and gene-editing experiments. Transgenic assays showed that both BdFTL1 and BdFTL2 could promote flowering, whereas BdFTL2 was essential for flowering initiation. Notably, BdFTL1 is subject to alternative splicing (AS), and its transcriptional level and AS are significantly affected by BdFTL2. Additionally, BdFTL2 could bind with the PHD-containing protein BdES43, an H3K4me3 reader. Furthermore, BdES43 was antagonistic to BdFTL2 in flowering initiation in a transcription-dependent manner and significantly affected BdFTL1 expression. BdFTL2, BdES43 and H3K4me3 also had highly similar distribution patterns within the BdFTL1 locus, indicating their interplay in regulating target genes. Taken together, florigen BdFTL2 functions as a potential epigenetic effector of BdFTL1 by interacting with a BdES43-H3K4me3 complex. This finding provides an additional insight for the regulatory mechanism underlying the multifaceted roles of florigen.

Genetic architecture underlying light and temperature mediated flowering in Arabidopsis, rice, and temperate cereals

“…Elevated expression of TaFT and HvFT promotes flowering significantly (Yan et al ., 2006; Lv et al ., 2014). Overexpression of FT orthologues greatly accelerates flowering, and their knockout mutants are late flowering in Brachypodium (Cao et al ., 2020).…”

“…Hd3a additionally interacts with 1433 (also named Gf14) protein in the cytoplasm to form a FAC with OsFD1, which then activates OsMADS15 , an AP1 homologue (Purwestri et al ., 2009; Taoka et al ., 2011; Kobayashi et al ., 2012). FD and 14‐3‐3 homologues can also interact with the FT homologues in wheat and Brachypodium (Li et al ., 2015; Cao et al ., 2020). However, the function of FD and 1433 homologues in flowering time in temperate grasses remains unknown.…”

“…CO and FT expression are controlled not only by quite a few positive and negative regulators, but also by multilayer regulatory control, providing an efficient and rapid means for plants to respond to light and temperature changes (Imaizumi, 2010; He et al ., 2020). FT, a major florigen physiologically, integrates internal and environmental signals to control flowering, and induction of flowering in response to its accumulation is highly conserved (Komiya et al ., 2008; Imaizumi, 2010; Cao et al ., 2020). FT is a small protein of only 23 kDa, which facilitates its transferability from leaves, the key tissue sensing light and temperature, to apical meristems.…”

“…FT is a small protein of only 23 kDa, which facilitates its transferability from leaves, the key tissue sensing light and temperature, to apical meristems. FT might also act as an epigenetic effector, indicative of its versatility and self‐regulation (Cao et al ., 2020). Overall, the CO–FT module is a prerequisite for timely flowering and normal reproduction, providing a convenient evolutionary solution when alterations in flowering time are needed.…”

“…Each conserved core component in the flowering pathway usually contains at least two functionally abundant or overlapping members, such as FT , CO , SVP , AP1 , and SOC1 (Dataset S1). There are FT ‐like genes with functional abundance in flowering, such as FT and TWIN SISTER OF FT ( TSF ) in Arabidopsis, Hd3a , RFT1 , and FTL1 in rice, and FT1 and FT2 in temperate grasses, which guarantee flowering initiation through alternative pathways (Cao et al ., 2020). For example, both FT and TSF promote flowering, and loss‐of‐function mutations of TSF enhance the late‐flowering phenotype of ft mutants in LD (Yamaguchi et al ., 2005).…”