Repression of flowering under a noninductive photoperiod by the HDA9‐AGL19‐FT module in Arabidopsis

Abstract

SummaryPosttranslational acetylation of histones is reversibly regulated by histone deacetylases (HDACs). Despite the evident significance of HDACs in Arabidopsis development, the biological roles and underlying molecular mechanisms of many HDACs are yet to be elucidated.By a reverse-genetic approach, we isolated an hda9 mutant and performed phenotypic analyses on it. In order to address the role of HDA9 in flowering, genetic, molecular, and biochemical approaches were employed.hda9 flowered early under noninductive short-day (SD) conditions and had increased expression of the floral integrator FLOWERING LOCUS T (FT) and the floral activator AGAMOUS-LIKE 19 (AGL19) compared with the wild-type. The hda9 mutation increased histone acetylation and RNA polymerase II occupancy at AGL19 but not at FT during active transcription, and the HDA9 protein directly targeted AGL19. AGL19 expression was higher under SD than under inductive long-day (LD) conditions, and an AGL19 overexpression caused a strong up-regulation of FT. A genetic analysis showed that an agl19 mutation is epistatic to the hda9 mutation, masking both the early flowering and the increased FT expression of hda9.Taken together, our data indicate that HDA9 prevents precocious flowering under SD conditions by curbing the hyperactivation of AGL19, an upstream activator of FT, through resetting the local chromatin environment.

POWERDRESS and HDA9 interact and promote histone H3 deacetylation at specific genomic sites in Arabidopsis

“…S3) (35, 36). The early flowering phenotype was much milder under continuous light compared with short-day conditions (35,36), such that pwr-2 and hda9-1 mutants bolted about 1.5 d earlier than wild type, with a similar number of rosette leaves to that in wild type at bolting (Fig. S3).…”

“…2B). Several studies have shown that early flowering in hda9 is because of increased AGL19 levels, which results from increased levels of histone acetylation and Pol II occupancy at the locus (35,36). To investigate whether PWR acts in the AGL19-mediated floweringtime pathway through HDA9 function, we first examined AGL19 transcript levels in pwr-2.…”

“…HDA9 regulates several biological processes, such as flowering time, seed dormancy, and stress responses (14,35,36,40,41). Although previous studies have shown that development and stress-response genes are up-regulated and this is accompanied by hyperacetylation in the hda9 mutant, there have been no reports about HDA9-interacting proteins required for its histone deacetylation function.…”

Histone Acetylation and Plant Development

“…4). In contrast, hda9 mutants display an early flowering phenotype under short-day conditions [33]. HDA9 directly represses the expression of AGOMOUS-LIKE 19 (AGL19), an upstream activator of FT through histone deacetylation.…”

Winter Memory throughout the Plant Kingdom: Different Paths to Flowering

“…AGL19, another MADS-box protein closely related to SOC1, might also play a role in the vernalization pathway, as the agl19 and flc mutations show additive impairment of the vernalization response (Schönrock et al, 2006). AGL19 appears to be a floral activator up-regulated upon cold exposure through FLC-independent processes (Schönrock et al, 2006;Kang et al, 2015). Although further work is needed to assess the role of these additional components in the vernalization response, a recent study suggests that they might participate in environmental adaptation as their differential regulation is correlated with the flowering time of different accessions originating from an altitudinal gradient (Suter et al, 2014).…”