Three dominant awnless genes in common wheat: Fine mapping, interaction and contribution to diversity in awn shape and length.

Motohiro Yoshioka,Julio C M Iehisa,Ryoko Ohno,Hiroyuki Enoki,Tatsuro Kimura,Shigeo Takumi,Shuhei Nasuda,Satoru Nishimura

doi:10.1371/journal.pone.0176148

Motohiro Yoshioka, Julio C M Iehisa + Show 6 more

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https://doi.org/10.1371/journal.pone.0176148

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Abstract

The awn is a long needle-like structure formed at the tip of the lemma in the florets of some grass species. It plays a role in seed dispersal and protection against animals, and can contribute to the photosynthetic activity of spikes. Three main dominant inhibitors of awn development (Hd, B1 and B2) are known in hexaploid wheat, but the causal genes have not been cloned yet and a genetic association with awn length diversity has been found only for the B1 allele. To analyze the prevalence of these three awning inhibitors, we attempted to predict the genotypes of 189 hexaploid wheat varieties collected worldwide using markers tightly linked to these loci. Using recombinant inbred lines derived from two common wheat cultivars, Chinese Spring and Mironovskaya 808, both with short awns, and a high-density linkage map, we performed quantitative trait locus analysis to identify tightly linked markers. Because this linkage map was constructed with abundant array-based markers, we converted the linked markers to PCR-based markers and determined the genotypes of 189 hexaploids. A significant genotype-phenotype correlation was observed at the Hd and B1 regions. We also found that interaction among these three awning inhibitors is involved in development of a membranous outgrowth at the base of awn resembling the Hooded mutants of barley. For the hooded awn phenotype, presence of the Hd dominant allele was essential but not sufficient, so B2 and other factors appear to act epistatically to produce the ectopic tissue. On the other hand, the dominant B1 allele acted as a suppressor of the hooded phenotype. These three awning inhibitors largely contribute to the genetic variation in awn length and shape of common wheat.

Highlights

The awn is a long needle-like structure formed on the distal end of the lemma in the florets of some grass species such as wheat, barley and rice
We performed quantitative trait locus (QTL) analysis for awn length using a high-resolution map constructed in our previous study [26] and identified three main QTLs for awn length at the top and middle of the spike located on chromosomes 4A, 5A and 6B (Table 1)
Important roles of awns in spike photosynthetic activity and seed dispersal have been suggested in wheat, the genes involved in awn development have not been identified

Summary

Introduction

The awn is a long needle-like structure formed on the distal end of the lemma in the florets of some grass species such as wheat, barley and rice. This extension of the lemma seems to be a modified leaf blade [1] and can serve to protect against animals [2]. Because the pathway for assimilate movement from awns to the kernels is minimal, the awns can be considered as an ideal place for light interception and CO2 uptake [7] These observations may contribute to the observation that the presence of awns can double the net rate of spike photosynthesis [8]. Awns have only a limited effect on yield in wet climates, their contribution is significantly higher than in awnless or deawned wheat varieties in drier conditions [9]

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