A Single Nucleotide Polymorphism of Nud Converts the Caryopsis Type of Barley (Hordeum Vulgare L.)

Abstract

Whether the caryopsis of barley is naked or covered is controlled by the Nud gene encoding an ethylene response factor (ERF) family transcription factor (TF) of the AP2/ERF TF superfamily that is involved in the lipid biosynthesis pathway. In covered barley, lipids on the surface of caryopses act as a glue for their tight adhesion with hulls. Separation of hulls in naked barley is due to the absence of surface lipids on caryopses. A natural deletion event of Nud was found to be the determinant of naked caryopsis and had been proposed as the monophyletic origin of domesticated naked barley. In the present study, we re-sequenced the nud locus in 162 barleys, comprising 79 covered and 83 naked barleys varieties. Besides the normal deletion mutation of Nud contributing to naked caryopsis, we found a novel allele of Nud, designated as nud1.g, distinctly in three naked barleys collected from Tibet. nud1.g contains a non-synonymous SNP T643A when compared with the functional Nud gene. Genetic analysis indicated that the SNP T643A of nud1.g co-segregates with the naked phenotype. The nud1.g gene was expressed normally in the three naked barleys. Furthermore, in silico prediction of functionally conserved sites and 3D structures showed that the amino acid substitution (valine to aspartate) caused by SNP T643A may lead to a dramatic structural alteration of NUD that may result in loss of function. This study provides evidence of a new origin of the naked phenotype of domesticated barley in Tibet.