The DTH8-Hd1 Module Mediates Day-Length-Dependent Regulation of Rice Flowering

Abstract

Photoperiodic flowering is one of the most important pathways to govern flowering in rice (Oryza sativa), in which Heading date 1 (Hd1), an ortholog of the Arabidopsis CONSTANS gene, encodes a pivotal regulator. Hd1 promotes flowering under short-day conditions (SD) but represses flowering under long-day conditions (LD) by regulating the expression of Heading date 3a (Hd3a), the FLOWERING LOCUS T (FT) ortholog in rice. However, the molecular mechanism of how Hd1 changes its regulatory activity in response to day length remains largely unknown. In this study, we demonstrated that the repression of flowering in LD by Hd1 is dependent on the transcription factor DAYS TO HEADING 8 (DTH8). Loss of DTH8 function results in the activation of Hd3a by Hd1, leading to early flowering. We found that Hd1 directly interacts with DTH8 and that the formation of the DTH8-Hd1 complex is necessary for the transcriptional repression of Hd3a by Hd1 in LD, implicating that the switch of Hd1 function is mediated by DTH8 in LD rather than in SD. Furthermore, we revealed that DTH8 associates with the Hd3a promoter to modulate the level of H3K27 trimethylation (H3K27me3) at the Hd3a locus. In the presence of the DTH8-Hd1 complex, the H3K27me3 level was increased at Hd3a, whereas loss of DTH8 function resulted in decreased H3K27me3 level at Hd3a. Taken together, our findings indicate that, in response to day length, DTH8 plays a critical role in mediating the transcriptional regulation of Hd3a by Hd1 through the DTH8-Hd1 module to shape epigenetic modifications in photoperiodic flowering.

Regulation of monocot and dicot plant development with constitutively active alleles of phytochrome B

“…In rice under non‐inductive LD conditions, phyB has been shown to delay flowering by up‐regulating Ghd7 , thereby inhibiting expression of the flowering signal integrator Ehd1 that promotes expression of florigen genes Hd3a and RFT1 (Itoh et al, 2010; Osugi et al, 2011; Xue et al, 2008). Another major photoperiodic regulator of Hd3a expression is the rice CONSTANS orthologue Hd1, which appears to promote or repress flowering in SD or LD, respectively (Du et al, 2017; Izawa et al, 2002). We hypothesize that OsPHYB / OsYHB overexpression triggers early flowering in rice by transcriptionally/translationally regulating the Ghd7‐Ehd1‐Hd3a/RFT1 pathway and/or Hd1 activity.…”

Ghd8 regulates rice photosensitivity by forming a complex that interacts with Ghd7

“…It has been reported that Hd1 is a key gene that largely determines rice photosensitivity [28]. Given that both Ghd7 and Ghd8 are involved in the Hd1-Hd3a regulatory pathway [25,29,30], we tested whether the interaction between Ghd7 and Ghd8 or Ghd7 and Ghd8 alone can affect the function of Hd1 on photosensitivity. The core collection was planted under both LD and SD conditions.…”

De novo sequencing of the transcriptome reveals regulators of the floral transition in Fargesia macclureana (Poaceae)

“…Previous results have indicated that the floral transition is orchestrated by several parallel and interactive genetic pathways that are regulated by a variety of environmental and endogenous signals [1]. Many key genes and regulatory networks have been identified in herbaceous annual plants such as Arabidopsis [2,3], rice [4], gourds [5], potato [6] and sorghum [7]. However, much less 3 is known about such regulation in perennial plants.…”