Mapping and candidate gene analysis of a QTL associated with leaf rolling index on chromosome 6D in bread wheat

Leaf rolling is an important morphological trait in wheat (Triticum aestivum L.) that is strongly correlated with photosynthesis, transpiration, and respiration, especially in abiotic stress conditions. The identification of quantitative trait loci (QTLs) and genes underlying leaf rolling is essential for wheat breeding. In this study, the ethyl methanesulfonate (EMS) induced mutant Y536 was isolated in a Nongda 3753 background with extreme abaxial leaf rolling. The F₂ and F_2:3 populations derived from a cross between Jing411 and mutant Y536 with contrasting leaf rolling morphologies were developed to map the locus controlling leaf rolling. A public SSR marker was isolated on chromosome 6DL that had a high linkage level with leaf rolling index (LRI). QTL analysis revealed a stable QTL associated with LRI, named QLRI.cau-6D, which explained 7.69 to 10.86% of the total phenotypic variation and had LOD scores ranging from 10.00 to 13.32. TraesCS6D02G237000 (TaHDZIV-D1) was identified as the priority candidate gene according to coding sequence differences between the two parents and gene functional annotations. Consistently, knocking out TaHDZIV-A1/B1/D1 in common wheat line ‘JW1’ significantly increased the LRI compared to the wild type, while overexpression of TaHDZIV-D1 in ‘JW1’ significantly reduced the LRI until the leaves rolled in the opposite direction. Moreover, genetic evidence suggested that TaHDZIV-A1/B1/D1 affects leaf rolling in a dose-dependent manner. Collectively, these findings provide novel insights into the genetic basis of leaf rolling in common wheat.