Abstract
Growing cultivated rice with a moderate heading date is the key to expanding its cultivation area and maintaining stable yields. The genes that regulate heading date are largely cloned; however, it remains unclear how genetic mutations and their combinations affect the heading date and adaptability of cultivated rice. Here, we report the analysis of genetic variation in eight long-day flowering suppressor genes (Hd1, DTH8, Ghd7, OsCOL4, DTH7, Hd6, Se5, and PhyB) and the phylogenetic relationship of eight genes. Genetic variations in DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are correlated with differences in heading date and the correlation between the genetic diversity of Hd6 and Se5 and rice heading data are weak. One group of haplotypes of DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are associated with earlier heading dates and appear to have accumulated during the northward expansion of rice cultivation. A minimum of four group A alleles of DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are required for the growth of cultivated rice at latitudes above 30°N. This study presents a preliminary investigation of the genetic patterns and adaptation mechanisms of long-day flowering suppressor genes and provides a useful reference for the molecular breeding of rice cultivars for various environments and farming systems.
Highlights
To make full use of sunlight and temperature resources and to ensure food security, it is necessary to selectively breed rice varieties whose heading dates are suited to the climatic characteristics of different regions (Itoh et al, 2018)
Sequence lengths ranged from 774 bp to 3516 bp, and 233 SNPs were found among all the sequences (25, 47, 41, 59, 30, 19, 10, and 2 SNPs in DTH8, Ghd7, Heading date 1 (Hd1), DTH7, PHYTOCHROME B (PhyB), OsCOL4, HEADING DATE 6 (Hd6), and Se5, respectively)
4, 2, 6, 3, 1, and 1 indels were identified in DTH8, DTH7, Ghd7, Hd1, PhyB, OsCOL4, and Hd6, respectively (Figure S3); there were no indels in Se5 (Figure S3)
Summary
To make full use of sunlight and temperature resources and to ensure food security, it is necessary to selectively breed rice varieties whose heading dates are suited to the climatic characteristics of different regions (Itoh et al, 2018). Heading date 1 (Hd1) and Early heading date 1 (Ehd1) are two hub genes in the photoperiodic regulatory pathway that have different responses to day length. They control the formation of florigen genes by receiving multiple regulatory signals from upstream genes and influencing heading date (Yano et al, 2000; Wei et al, 2016). Under short-day conditions, Ehd is regulated by multiple upstream genes that include OsGIGANTEA (OsGI), Early heading date 2 (Ehd2), and MADS BOX GENE 51 (OsMAD51) (Matsubara et al, 2008; Ryu et al, 2009). The photoperiodic regulatory network in cultivated rice can be divided into short-day promotion, long-day promotion, and long-day suppression pathways
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