Evolutionary history of the NAM-B1 gene in wild and domesticated tetraploid wheat

Maria Lundström,Matti W Leino,Jenny Hagenblad

doi:10.1186/s12863-017-0566-7

Maria Lundström, Matti W Leino + Show 1 more

Open Access

https://doi.org/10.1186/s12863-017-0566-7

Copy DOI

Abstract

BackgroundThe NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size. First detected in wild emmer wheat, the wild-type allele of the gene has been introgressed into durum and bread wheat. Later studies have, however, also found the presence of the wild-type allele in some domesticated subspecies. In this study we trace the evolutionary history of the NAM-B1 in tetraploid wheat species and evaluate it as a putative domestication gene.ResultsGenotyping of wild and landrace tetraploid accessions showed presence of only null alleles in durum. Domesticated emmer wheats contained both null alleles and the wild-type allele while wild emmers, with one exception, only carried the wild-type allele. One of the null alleles consists of a deletion that covers several 100 kb. The other null-allele, a one-basepair frame-shift insertion, likely arose among wild emmer. This allele was the target of a selective sweep, extending over several 100 kb.ConclusionsThe NAM-B1 gene fulfils some criteria for being a domestication gene by encoding a trait of domestication relevance (seed size) and is here shown to have been under positive selection. The presence of both wild-type and null alleles in domesticated emmer does, however, suggest the gene to be a diversification gene in this species. Further studies of genotype-environment interactions are needed to find out under what conditions selection on different NAM-B1 alleles have been beneficial.

Highlights

The NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size
The circumstances surrounding the domestication of the tetraploid wheats, resulting in domesticated emmer (Triticum turgidum subsp. dicoccum) and durum wheat (Triticum turgidum subsp. durum), have long been debated
The tetraploid accessions were chosen so that, whenever possible, different genotypes were represented among the different subspecies: ten domesticated emmers with WT and ten with +1 bp allele, ten wild emmers with WT and one with +1 bp, and nine durum wheats all of which carried the +1 bp allele

Summary

Introduction

The NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size. In this study we trace the evolutionary history of the NAM-B1 in tetraploid wheat species and evaluate it as a putative domestication gene. The process originated in the Fertile Crescent, where stands of wild tetraploid emmer The circumstances surrounding the domestication of the tetraploid wheats, resulting in domesticated emmer Some studies suggest a monophyletic origin of domesticated wheat [4, 5], possibly with gene flow between wild and domesticated populations [5], while others propose a polyphyletic origin [6, 7]. More recently it has been suggested that domesticated tetraploid wheats arose from a mixed set of wild emmer populations [8].

Methods

Results

Discussion

Conclusion