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Plants must accurately integrate external environmental signals with their own development to initiate flowering at the appropriate time for reproductive success. Photoperiod and temperature are key external signals that determine flowering time; both are cyclical and periodic, and they are closely related. In this review, we describe photoperiod-sensitive genes that simultaneously respond to temperature signals in rice (Oryza sativa). We introduce the mechanisms by which photoperiod and temperature synergistically regulate heading date and regional adaptation in rice. We also discuss the prospects for designing different combinations of heading date genes and other cold tolerance or thermo-tolerance genes to help rice better adapt to changes in light and temperature via molecular breeding to enhance yield in the future. [ABSTRACT FROM AUTHOR]

SUMMARY: Rice (Oryza sativa L.) is a short‐day plant whose heading date is largely determined by photoperiod sensitivity (PS). Many parental lines used in hybrid rice breeding have weak PS, but their F1 progenies have strong PS and exhibit an undesirable transgressive late‐maturing phenotype. However, the genetic basis for this phenomenon is unclear. Therefore, effective methods are needed for selecting parents to create F1 hybrid varieties with the desired PS. In this study, we used bulked segregant analysis with F1 Ningyou 1179 (strong PS) and its F2 population, and through analyzing both parental haplotypes and PS data for 918 hybrid rice varieties, to identify the genetic basis of transgressive late maturation which is dependent on dominance complementation effects of Hd1, Ghd7, DTH8, and PRR37 from both parents rather than from a single parental genotype. We designed a molecular marker‐assisted selection system to identify the genotypes of Hd1, Ghd7, DTH8, and PRR37 in parental lines to predict PS in F1 plants prior to crossing. Furthermore, we used CRISPR/Cas9 technique to knock out Hd1 in Ning A (sterile line) and Ning B (maintainer line) and obtained an hd1‐NY material with weak PS while retaining the elite agronomic traits of NY. Our findings clarified the genetic basis of transgressive late maturation in hybrid rice and developed effective methods for parental selection and gene editing to facilitate the breeding of hybrid varieties with the desired PS for improving their adaptability. Significance Statement: We identified the genetic basis of transgressive late maturation in hybrid rice, which is dependent on dominance complementation effects of Hd1, Ghd7, DTH8, and PRR37 from both parents and developed effective methods for parental selection and gene editing to facilitate the breeding of hybrid varieties with the desired photoperiod sensitivity. Our study lays an important foundation for improving the breeding efficiency and latitude adaptability of hybrid rice. [ABSTRACT FROM AUTHOR]

Summary: Rice (Oryza sativa) is a short‐day (SD) plant originally having strong photoperiod sensitivity (PS), with SDs promoting and long days (LDs) suppressing flowering. Although the evolution of PS in rice has been extensively studied, there are few studies that combine the genetic effects and underlying mechanism of different PS gene combinations with variations in PS.We created a set of isogenic lines among the core PS‐flowering genes Hd1, Ghd7 and DTH8 using CRISPR mutagenesis, to systematically dissect their genetic relationships under different day‐lengths. We investigated their monogenic, digenic, and trigenic effects on target gene regulation and PS variation.We found that Hd1 and Ghd7 have the primary functions for promoting and repressing flowering, respectively, regardless of day‐length. However, under LD conditions, Hd1 promotes Ghd7 expression and is recruited by Ghd7 and/or DTH8 to form repressive complexes that collaboratively suppress the Ehd1‐Hd3a/RFT1 pathway to block heading, but under SD conditions Hd1 competes with the complexes to promote Hd3a/RFT1 expression, playing a tradeoff relationship with PS flowering. Natural allelic variations of Hd1, Ghd7 and DTH8 in rice populations have resulted in various PS performances.Our findings reveal that rice PS flowering is controlled by crosstalk of two modules – Hd1–Hd3a/RFT1 in SD conditions and (Hd1/Ghd7/DTH8)–Ehd1–Hd3a/RFT1 in LD conditions – and the divergences of these genes provide the basis for rice adaptation to broad regions. [ABSTRACT FROM AUTHOR]