MicroRNA-resistant alleles of HOMEOBOX DOMAIN-2 modify inflorescence branching and increase grain protein content of wheat

Abstract

Plant and inflorescence architecture determine the yield potential of crops. Breeders have harnessed natural diversity for inflorescence architecture to improve yields, and induced genetic variation could provide further gains. Wheat is a vital source of protein and calories; however, little is known about the genes that regulate the development of its inflorescence. Here, we report the identification of semidominant alleles for a class III homeodomain-leucine zipper transcription factor, HOMEOBOX DOMAIN-2 ( HB-2 ), on wheat A and D subgenomes, which generate more flower-bearing spikelets and enhance grain protein content. These alleles increase HB-2 expression by disrupting a microRNA 165/166 complementary site with conserved roles in plants; higher HB-2 expression is associated with modified leaf and vascular development and increased amino acid supply to the inflorescence during grain development. These findings enhance our understanding of genes that control wheat inflorescence development and introduce an approach to improve the nutritional quality of grain.

FIND-IT: Accelerated trait development for a green evolution

“…Such genetic variants of GRF4 and SLN1/DELLA identified in modern green revolution varieties enable crosses and field trials aimed at generating new elite barley varieties with enhanced nitrogen use efficiency and hence reduced requirements for nitrogenous fertilizers ( 36 ). MiRNA-resistant alleles of the HOMEOBOX DOMAIN-2 ( HB-2 ) gene in wheat have recently been shown to result in increased HB-2 transcript levels, further highlighting the usefulness of targeting single-base changes in miRNA -binding sites to fine-regulate gene transcript abundance ( 37 ).…”

Recent advances in the genetics underlying wheat grain protein content and grain protein deviation in hexaploid wheat

“…The introgression of a high molecular weight glutenin subunit (HMW-GS) allele led to an increase in wheat GPC and even yield, and induced changes in the abundance of other grain storage proteins (Cao et al 2021). The increased expression of the microRNA-resistant alleles of a class III homeodomain-leucine-zipper transcription factor HOMEOBOX DOMAIN-2 (HB-2) located on chromosome 1 of subgenomes A and D, was shown to increase GPC through increasing amino acid supply during grain development and independent of the senescence pathway (Dixon et al 2022). These results highlight different mechanisms converging on GPC, together with the possibility of identifying GPC regulators in different pathways.…”

Form follows function in Triticeae inflorescences

“…In the gain-of-function wheat TB1 alleles, the TB1 protein competitively binds to FT1, making it less available to promote meristem maturation ( Dixon et al 2018 ). In another study, Dixon et al (2022) showed that semidominant alleles of the wheat A and D homoeologous genes encoding the class III homeodomain-leucine zipper TF HOMEOBOX DOMAIN-2 (HB-2) promote SS formation. In contrast to the previous mechanisms, the regulation of SS formation by HB-2 is modulated through microRNA-based regulation; in the semi-dominant alleles of HB-2 , the complementary microRNA165/166 ( miR165/166 ) binding site is disrupted, leading to elevated levels of HB-2 transcripts known to promote leaf and vascular development and increase the amino acid supply required for grain development in the SS ( Dixon et al 2022 ).…”