Effects of the core heading date genes Hd1, Ghd7, DTH8, and PRR37 on yield-related traits in rice

We clarify the influence of the genotypes of the heading date genes Hd1, Ghd7, DTH8, and PRR37 and their combinations on yield-related traits and the functional differences between different haplotypes. Heading date is a key agronomic trait in rice (Oryza sativa L.) that determines yield and adaptability to different latitudes. Heading date 1 (Hd1), Grain number, plant height, and heading date 7 (Ghd7), Days to heading on chromosome 8 (DTH8), and PSEUDO-RESPONSE REGULATOR 37 (PRR37) are core rice genes controlling photoperiod sensitivity, and these genes have many haplotypes in rice cultivars. However, the effects of different haplotypes at these genes on yield-related traits in diverse rice materials remain poorly characterized. In this study, we knocked out Hd1, Ghd7, DTH8, or PRR37, alone or together, in indica and japonica varieties and systematically investigated the agronomic traits of each knockout line. Ghd7 and PRR37 increased the number of spikelets and improved yield, and this effect was enhanced with the Ghd7 DTH8 or Ghd7 PRR37 combination, but Hd1 negatively affected yield. We also identified a new weak functional Ghd7 allele containing a mutation that interferes with splicing. Furthermore, we determined that the promotion or inhibition of heading date by different PRR37 haplotypes is related to PRR37 expression levels, day length, and the genetic background. For rice breeding, a combination of functional alleles of Ghd7 and DTH8 or Ghd7 and PRR37 in the hd1 background can be used to increase yield. Our study clarifies the effects of heading date genes on yield-related traits and the functional differences among their different haplotypes, providing valuable information to identify and exploit elite haplotypes for heading date genes to breed high-yielding rice varieties.