The extensive utilization of two alleles Rht-B1b and Rht-D1b at Rht-1 loci in wheat gave rise to drastic increases in yields triggering the so-called "Green Revolution".Here,a new natural allelic variation Rht-B1i which contains a single missense SNP(A614G)in the coding region was found to significantly increase plant height under both Rht-D1a(11.68%)and Rht-D1b(7.89%)background.To elucidate the molecular mechanism of Rht-B1i,investigations on the promoter of Rht-B1i were carried out.Sequence analysis showed the promoter of Rht-B1i could be divided into two classes,one contained a specific 160 bp insertion,the other without 160 bp insertion in promoter,thus divided Rht-B1i into Rht-B1i-1(with 160 bp insertion in promoter)and Rht-B1i-2(without 160 bp insertion in promoter)genotypes.The promoter of Rht-B1i-1 had 32 more possible cis-acting elements than that of Rht-B1a,including a unique auxin response element AUXREPSIAA4.Quantitative RT-PCR analysis indicated that 160 bp insertion could affect the transcription of Rht-B1i gene.The coleoptile lengths of wheat varieties treated with IAA,GA3 and IAA/GA3,together with the histochemical staining of Rht-B1i-1 promoter transgenic Arabidopsis illustrated that the height-prompting effect of Rht-B1i-1 might be caused by the synergistic action of IAA and GA3.These results add new information to help in understanding the regulatory mechanism of Rht-1 in wheat and provide new gene resources for wheat genetic improvement.