Identification of the causal mutation in early heading mutant of bread wheat (Triticum aestivum L.) using MutMap approach

In bread wheat ( Triticum aestivum L.), fine-tuning the heading time is essential to maximize grain yield. Photoperiod-1 ( Ppd-1 ) and VERNALIZATION 1 ( Vrn-1 ) are major genes affecting photoperiod sensitivity and vernalization requirements, respectively. These genes have predominantly governed heading timing. However, Ppd-1 and Vrn-1 significantly impact heading dates, necessitating another gene that can slightly modify heading dates for fine-tuning. In this study, we developed an early heading mutant from the ethyl methanesulfonate-mutagenized population of the Japanese winter wheat cultivar “Kitahonami.” MutMap analysis identified a nonsense mutation in the clock component gene Wheat PHYTOCLOCK 1/LUX ARRHYTHMO ( WPCL-D1 ) as the probable SNP responsible for the early heading mutant on chromosome 3D. Segregation analysis using F 2 and F 3 populations confirmed that plants carrying the wpcl-D1 allele headed significantly earlier than those with the functional WPCL-D1 . The early heading mutant exhibited increased expression levels of Ppd-1 and circadian clock genes, such as WPCL1 and LATE ELONGATED HYPOCOTYL ( LHY ). Notably, the transcript accumulation levels of Ppd-A1 and Ppd-D1 were influenced by the copy number of the functional WPCL1 gene. These results suggest that a loss-of-function mutation in WPCL-D1 is the causal mutation for the early heading phenotype. Adjusting the functional copy number of WPCL1 will be beneficial in fine-tuning of heading dates.