A Combination of Long-Day Suppressor Genes Contributes to the Northward Expansion of Rice

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 (<i>Hd1, DTH8, Ghd7, OsCOL4, DTH7, Hd6, Se5</i>, and <i>PhyB</i>) and the phylogenetic relationship of eight genes. Genetic variations in <i>DTH8</i>, <i>Ghd7</i>, <i>Hd1</i>, <i>DTH7</i>, <i>PhyB</i>, and <i>OsCOL4</i> are correlated with differences in heading date and the correlation between the genetic diversity of <i>Hd6</i> and <i>Se5</i> and rice heading data are weak. One group of haplotypes of <i>DTH8</i>, <i>Ghd7</i>, <i>Hd1</i>, <i>DTH7</i>, <i>PhyB</i>, and <i>OsCOL4</i> 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 <i>DTH8</i>, <i>Ghd7</i>, <i>Hd1</i>, <i>DTH7</i>, <i>PhyB</i>, and <i>OsCOL4</i> 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.