High molecular weight glutenin subunits (HMW-GS), major components of seed storage proteins in wheat, have large effects on processing quality. GLU-1 genes encode HMW-GS and their expression is mainly controlled at the transcriptional level by interactions between cis-regulatory elements and transcription factors. We previously identified an Aux/IAA transcription factor TaIAA10-6D that bound to a conserved cis-regulatory module CCRM1-1, the most essential conserved cis-regulatory module in GLU-1. Here, we confirmed the binding of TaIAA10-6D to CCRM1-1 using yeast one hybrid and dual-luciferase reporter assays. The enhanced expression of TaIAA10-6D suppressed glutenin accumulation and increased gliadin content. Dynamic transcriptome analyses revealed that TaIAA10-6D overexpression down-regulated glutenin and gliadin genes during an early stage of grain filling, but up-regulated gliadin genes during a late stage probably by endoplasmic reticulum stress, accounting for its effect on the trade-off between glutenin and gliadin. Rheological property and processing quality assays showed that TaIAA10-6D overproduction reduced stabilization time and bread quality, but enhanced cookie quality. Overexpression of TaIAA10-6D also reduced plant height, leaf size, kernel number and grain yield. We identified two major haplotypes of TaIAA10-6D, Hap Ⅰ and Hap Ⅱ, and developed a breeding-friendly diagnostic marker. Hap Ⅰ conferred higher expression of TaIAA10-6D and concomitantly reduced plant height and kernel number, but had little effect on grain yield, contributing to lodging resistance without yield penalty. Hap Ⅰ was subjected to positive selection in breeding. The findings provide a useful gene for wheat improvement and broaden insights into the regulatory machinery underpinning auxin-mediated quality formation, plant morphogenesis and yield gain.

Grain weight and grain number are important yield component traits in wheat and identification of underlying genetic loci is helpful for improving yield. Here, we identified eight stable quantitative trait loci (QTL) for yield component traits, including five loci for thousand grain weight (TGW) and three for grain number per spike (GNS) in a recombinant inbred line population derived from cross Yangxiaomai/Zhongyou 9507 across four environments. Since grain size is a major determinant of grain weight, we also mapped QTL for grain length (GL) and grain width (GW). QTGW.caas-2D, QTGW.caas-3B, QTGW.caas-5A and QTGW.caas-7A.2 for TGW co-located with those for grain size. QTGW.caas-2D also had a consistent genetic position with QGNS.caas-2D, suggesting that the pleiotropic locus is a modulator of trade-off effect between TGW and GNS. Sequencing and linkage mapping showed that TaGL3-5A and WAPO-A1 were candidate genes of QTGW.caas-5A and QTGW.caas-7A.2, respectively. We developed Kompetitive allele specific PCR (KASP) markers linked with the stable QTL for yield component traits and validated their genetic effects in a diverse panel of wheat cultivars from the Huang-Huai River Valley region. KASP-based genotyping analysis further revealed that the superior alleles of all stable QTL for TGW but not GNS were subject to positive selection, indicating that yield improvement in the region largely depends on increased TGW. Comparative analyses with previous studies showed that most of the QTL could be detected in different genetic backgrounds, and QTGW.caas-7A.1 is likely a new QTL. These findings provide not only valuable genetic information for yield improvement but also useful tools for marker-assisted selection.

Wheat high-molecular-weight glutenin subunits (HMW-GS) determine dough elasticity and play an essential role in processing quality. HMW-GS are encoded by Glu-1 genes and controlled primarily at transcriptional level, implemented through the interactions between cis-acting elements and trans-acting factors. However, transcriptional mechanism of Glu-1 genes remains elusive. Here we made a comprehensive analysis of cis-regulatory elements within 1-kb upstream of the Glu-1 start codon (−1000 to −1) and identified 30 conserved motifs. Based on motif distribution pattern, three conserved cis-regulatory modules (CCRMs), CCRM1 (−300 to −101), CCRM2 (−650 to −400), and CCRM3 (−950 to −750), were defined, and their functions were characterized in wheat stable transgenic lines transformed with progressive 5′ deletion promoter::GUS fusion constructs. GUS staining, qPCR and enzyme activity assays indicated that CCRM2 and CCRM3 could enhance the expression level of Glu-1, whereas the 300-bp promoter (−300 to −1), spanning CCRM1 and core region (−100 to −1), was enough to ensure accurate Glu-1 initiation at 7 days after flowering (DAF) and shape its spatiotemporal expression pattern during seed development. Further transgenic assays demonstrated that CCRM1-2 (−300 to −209) containing Complete HMW Enhancer (−246 to −209) was important for expression level but had no effect on expression specificity in the endosperm. In contrast, CCRM1-1 (−208 to −101) was critical for both expression specificity and level of Glu-1. Our findings not only provide new insights to uncover Glu-1 transcription regulatory machinery but also lay foundations for modifying Glu-1 expression.