Identification and validation of a major gene for kernel length at the P1 locus in Triticum polonicum

Kernel size, one of the traits that determine wheat yield, is controlled by multiple quantitative trait loci. Polish wheat ( Triticum polonicum ) has elongated and plump kernel and is a valuable material for breeding high-yielding wheat cultivars. However, genes or loci determining kernel length (KL) in Polish wheat are unknown. We identified and validated a major KL gene, KL-PW , at the P1 locus in Polish wheat. KL-PW is VRT-A2 , which encodes a MIKC-type MADS-box protein (MADS55). An insertion/deletion mutation in intron 1 of VRT-A2 PW led to an alternatively spliced transcript, VRT-A2 PW2 . Quantitative PCR analysis showed that VRT-A2 PW was more highly expressed in developing seeds than was VRT-A2 Ailanmai . Brassinosteroid (BR) sensitivity experiment and the expression of BR-related genes indicated that VRT-A2 PW functions as a positive regulator of BR responses. VRT-A2 PW significantly increased KL of wheat. These findings not only reveal the molecular basis of KL-PW in controlling KL, but also provide a valuable genetic resource for increasing kernel size in wheat.