摘要Polish wheat(Triticum polonicum)is a unique tetraploid wheat species characterized by an elongated outer glume.The genetic control of the long-glume trait by a single semi-dominant locus,P1(from Polish wheat),was established more than 100 years ago,but the underlying causal gene and molecular nature remain elusive.Here,we report the isolation of VRT-A2,encoding an SVP-clade MADS-box transcription factor,as the P1 candidate gene.Genetic evidence suggests that in T.polonicum,a naturally occurring sequence rearrange-ment in the intron-1 region of VRT-A2 leads to ectopic expression of VRT-A2 in floral organs where the long-glume phenotype appears.Interestingly,we found that the intron-1 region is a key ON/OFF molecular switch for VRT-A2 expression,not only because it recruits transcriptional repressors,but also because it confers intron-mediated transcriptional enhancement.Genotypic analyses using wheat accessions indicated that the P1 locus is likely derived from a single natural mutation in tetraploid wheat,which was subsequently in-herited by hexapioid T.petropavlovskyi.Taken together,our findings highlight the promoter-proximal intron variation as a molecular basis for phenotypic differentiation,and thus species formation in Triticum plants.