Dominant inhibition of awn development by a putative zinc-finger transcriptional repressor expressed at the B1 locus in wheat.

Tancey Melchkart,David J F Konkin,Yasmina Bekkaoui,Andrew Steed,Frank M You,Sateesh Kagale,Paul Nicholson,Adrian J Cutler,Catherine Chinoy,Nikolai M Adamski,J Allan Feurtado,Daiqing Huang,Martial Martucci,Qian Zheng,Curt A Mccartney,Martha Clarke

doi:10.1111/nph.16154

Abstract

Summary Awns, bristle‐like structures extending from grass lemmas, provide protection against predators, contribute to photosynthesis and aid in grain dispersal. In wheat, selection of awns with minimal extension, termed awnletted, has occurred during domestication by way of loci that dominantly inhibit awn development, such as Tipped1 (B1), Tipped2 (B2), and Hooded (Hd). Here we identify and characterize the B1 gene. B1 was identified using bulked segregant RNA‐sequencing of an F2 durum wheat population and through deletion mapping of awned bread wheat mutants. Functional characterization was accomplished by gene overexpression while haplotype analyses assessed B1 polymorphisms and genetic variation.Located on chromosome 5A, B1 is a C2H2 zinc finger encoding gene with ethylene‐responsive element binding factor‐associated amphiphilic repression (EAR) motifs. Constitutive overexpression of B1 in awned wheat produced an awnletted phenotype with pleiotropic effects on plant height and fertility. Transcriptome analysis of B1 overexpression plants suggests a role as transcriptional repressor, putatively targeting pathways involved in cell proliferation. Haplotype analysis revealed a conserved B1 coding region with proximal polymorphisms and supported the contention that B1 is mainly responsible for awnletted wheats globally. B1, predominantly responsible for awn inhibition in wheat, encodes a C2H2 zinc finger protein with EAR motifs which putatively functions as a transcriptional repressor.

Highlights

Awns are bristle-like structures extending from the lemma-tipmidvein in the Poaceae grasses including cereal crop species such as wheat (Triticum aestivum and T. durum), barley (Hordeum vulgare) and rice (Oryza sativa)
As a strategy to identify traits and genes associated with productivity under water stress, a biparental durum wheat population was developed from the cross of the Canadian cultivar Strongfield and the Australian Glossy Huguenot cultivar, which is further denoted as STxGH (Johnson et al, 1983; Clarke et al, 2005)
As demonstrated by the companion paper in this issue, DeWitt et al (2020), and consistent with the previous studies in rice, barley and wheat discussed in the Introduction above, awn presence in STxGH promoted increases in grain size and in particular grain length (Fig. 1d,e)

Summary

Introduction

Awns are bristle-like structures extending from the lemma-tipmidvein in the Poaceae grasses including cereal crop species such as wheat (Triticum aestivum and T. durum), barley (Hordeum vulgare) and rice (Oryza sativa). The grain dispersal functionality of awns has been lost during domestication in cereals due to inclusion of the nonshattering trait which is controlled by, amongst others, the Tenacious glumes (Tg) locus and the Q allele in wheat or naked caryopsis (nud) and thresh-1 genes in barley (Haas et al, 2019). A general reduction in grain-dispersal-aiding appendages such as awns, barbs and hairs has accompanied domestication (Fuller & Allaby, 2009). Wheat and barley awns have been retained to a great extent in domesticated cultivars, the awns are shorter, thinner and lighter than those of their wild progenitors (Peleg et al, 2010; Haas et al, 2019). Awns in wheat and barley contribute to photosynthesis and can promote yield in warmer and drier rainfed

Methods

Results

Discussion

Conclusion