OsPRR37 Alternatively Promotes Heading Date Through Suppressing the Expression of Ghd7 in the Japonica Variety Zhonghua 11 under Natural Long-Day Conditions

Abstract

Heading date is an important agronomic trait of rice (Oryza sativa L.) and is regulated by numerous genes, some of which exhibit functional divergence in a genetic background-dependent manner. Here, we identified a late heading date 7 (lhd7) mutant that flowered later than wild-type Zhonghua 11 (ZH11) under natural long-day (NLD) conditions. Map-based cloning facilitated by the MutMap strategy revealed that LHD7 was on the same locus as OsPRR37 but exhibited a novel function as a promoter of heading date. A single-nucleotide mutation of G-to-A in the coding region caused a substitution of aspartic acid for glycine at site 159 within the pseudo-receiver (PR) domain of OsPRR37. Transcriptional analysis revealed that OsPRR37 suppressed Ghd7 expression in both ZH11 background under NLD conditions and the Zhenshan 97 background under natural short-day conditions. Consistently, the expression of Ehd1, Hd3a and RFT1 was enhanced by OsPRR37 in the ZH11 background. Genetic analysis indicated that the promotion of heading date and reduction in grain yield by OsPRR37 were partially dependent on Ghd7. Further investigation showed that the alternative function of OsPRR37 required an intact Ghd7-related regulatory pathway involving not only its upstream regulators OsGI and PhyB but also its interacting partner Hd1. Our study revealed the distinct role of OsPRR37 in the ZH11 background, which provides a more comprehensive understanding of OsPRR37 function and enriches the theoretical bases for improvement of rice heading date in the future.

Natural alleles of CIRCADIAN CLOCK ASSOCIATED1 contribute to rice cultivation by fine-tuning flowering time

“…Third, OsCCA1 does not bind to the Ehd1 promoter for floral induction. OsPRR37 and DTH8 are LD-dependent floral repressors that contribute to the generation of robust Ehd1 mRNA oscillations ( Wei et al, 2010 ; Koo et al, 2013 ; Liu et al, 2018 ; Hu et al, 2021 ). Furthermore, since OsPRR37 is epistatic to OsCCA1 ( Supplemental Figure S9 ), it is possible that OsCCA1 induces Ehd1 expression by downregulating OsPRR37 or DTH8 , although further studies are required to verify the molecular mechanisms of OsCCA1 regulation.…”

“…The components of the circadian clock that are conserved between Arabidopsis and rice are integrated into the photoperiodic flowering network ( Song et al, 2015 ). Among them, we previously showed that rice OsPRR37 , which is orthologous to Arabidopsis PRR7 , suppresses flowering under LD conditions by downregulating Ehd1 and Hd3a expression ( Koo et al, 2013 ; Liu et al, 2018 ; Hu et al, 2021 ). Natural alleles with amino acid (aa) substitutions in the CCT domain of OsPRR37 promote flowering for adaptation to high-latitude regions ( Koo et al, 2013 ).…”

CG and CHG Methylation Contribute to the Transcriptional Control of OsPRR37-Output Genes in Rice

“…The OsPRR37 protein can interact with Ghd8 and NF-YCs, which form an alternative OsNF-Y heterotrimer to affect Hd1-mediated regulation of Hd3a and flowering ( Goretti et al, 2017 ). The distinct role of OsPRR37 in the ZH11 background indicated that OsPRR37 can associate with different partners to perform different functions ( Hu et al, 2021 ). Moreover, the 35 identified differentially methylated DEGs accounted for only a small proportion of DEGs ( Figure 5A ).…”

“…OsPRR37 was primarily identified to delay the flowering time and increase grain yield and adaptation in rice ( Koo et al, 2013 ; Liu et al, 2013 , 2015 ; Yan et al, 2013 ; Gao et al, 2014 ; Fujino et al, 2019 ). A recent study further revealed a distinct role of OsPRR37 in promoting flowering in the japonica variety Zhonghua 11 under natural long-day conditions ( Hu et al, 2021 ). Although several output genes involved in the photoperiodic flowering pathway are used to explain the trait variations ( Chen et al, 2021 ; Zhou et al, 2021c ), the underlying mechanism of how OsPRR37 regulates its output genes and multiple traits remains unclear.…”

Bifunctional regulators of photoperiodic flowering in short day plant rice

“…However, OsPRR37 could also function as a flowering promoter in cv. Zhonghua 11 (ZH11) background, mainly by inhibited Ghd7 expression ( Hu et al., 2021 ) ( Figure 5C ). Furthermore, OsPRR37 could act as an activator or a suppressor depending on the status of three genes, Ghd7 , DTH8 , and Hd1 ( Zhang et al., 2019 ).…”