Grain number and size are important agronomic traits determining grain yield, and yield improvement depends on exploring functional variations of key regulatory genes. Mitogen-activated protein kinase 6 (MAPK6) plays a key role in crop development; however, its function and variation in wheat remain largely unclear. In this study, we aimed to characterize the function and haplotype variations of TaMAPK6-7A in wheat and develop functional molecular markers for marker assisted breeding. We identified three TaMAPK6 homoeologs on 7A, 7B, and 7D in wheat through bioinformatics analysis and revealed their evolutionary trajectory by phylogenetic analysis, with clear monocot-dicot lineage divergence and TaMAPK6 homoeolog clustering matching with hexaploid wheat’s allopolyploid origin. Spatiotemporal expression analysis showed that the TaMAPK6 homoeologs constitutively expressed in wheat tissues and were highly abundant in endosperm, spike, grain, and anther, with TaMAPK6-7A showing slightly higher transcript levels. In an ethyl methanesulfonate (EMS)-induced Jing411 mutant library, we identified a loss-of-function mutant of TaMAPK6-7A (J7633452), which exhibited severely reduced grain number per spike, impaired anther fertility, and increased grain size. Natural variation analysis of a large set of wheat accessions identified two major haplotypes of TaMAPK6-7A, with Type I was identical to the reference genome cultivar ‘Chinese Spring’, and Type II was consistent with the elite wheat cultivar ‘AK58’. We developed a PCR marker to accurately distinguish the two haplotypes and genotyped 192 wheat cultivars and elite breeding lines. Phenotypic evaluation indicated that Type II was an elite haplotype significantly associated with higher grain number per spike. This study characterizes TaMAPK6-7A as a key regulator of grain number per spike, providing a gene and molecular marker for marker-assisted breeding to improve grain yield.
Lu et al. (Thu,) studied this question.