Fine mapping of the reduced height gene Rht22 in tetraploid wheat landrace Jianyangailanmai (Triticum turgidum L.).

KEY MESSAGE: Rht22 was fine mapped in the interval of 0.53-1.48 Mb on 7AS, which reduces cell number of internode to cause semi-dwarfism in Jianyangailanmai. As a valuable germplasm resource for wheat genetic improvement, tetraploid wheat has several reduced height (Rht) and enhanced harvest index genes. Rht22, discovered in Jianyangailanmai (JAM, Triticum turgidum L., 2n = 4x = 28, AABB), significantly increases the spikelet number per spike, but its accurate chromosomal position is still unknown. In this study, a high-density genetic map was constructed using specific-length amplified fragment sequencing in an F7 RIL_DJ population, which was derived from a cross between dwarf Polish wheat (T. polonicum L., 2n = 4x = 28, AABB) and JAM. Two plant height loci, Qph.sicau-4B and Qph.sicau-7A, were mapped on chromosomes 4BS and 7AS, respectively. Qph.sicau-7A was mapped to the 0.33-4.46 Mb interval on 7AS and likely represents the candidate region of Rht22. Fine mapping confirmed and narrowed Rht22 on chromosome arm 7AS between Xbag295.s53 and Xb295.191 in three different populations. The physical region ranged from 0.53 to 1.48 Mb and included 18 candidate genes. Transcriptome analysis of two pairs of near-isogenic lines revealed that 135 differentially expressed genes (DEGs) were associated with semi-dwarfism. Of these, the expression of 83 annotated DEGs involved in hormones synthesis and signal transduction, cell wall composition, DNA replication, microtubule and phragmoplast arrays was significantly down-regulated in the semi-dwarf line. Therefore, Rht22 causes semi-dwarfism in JAM by disrupting these cellular processes, which impairs cell proliferation and reduces internode cell number.