Arthur Cross, John B. Li, Robbie Waugh, Agnieszka A. Golicz & Mohammad Pourkheirandish

Theoretical and Applied Genetics April 2022; vol. 135: 1263–1277

Key message

Grain disarticulation in wild progenitor of wheat and barley evolved through a local duplication event followed by neo-functionalization resulting from changes in location of gene expression.

Abstract

One of the most critical events in the process of cereal domestication was the loss of the natural mode of grain dispersal. Grain dispersal in barley is controlled by two major genes, Btr1 and Btr2, which affect the thickness of cell walls around the disarticulation zone. The barley genome also encodes Btr1-like and Btr2-like genes, which have been shown to be the ancestral copies. While Btr and Btr-like genes are non-redundant, the biological function of Btr-like genes is unknown. We explored the potential biological role of the Btr-like genes by surveying their expression profile across 212 publicly available transcriptome datasets representing diverse organs, developmental stages and stress conditions. We found that Btr1-like and Btr2-like are expressed exclusively in immature anther samples throughout Prophase I of meiosis within the meiocyte. The similar and restricted expression profile of these two genes suggests they are involved in a common biological function. Further analysis revealed 141 genes co-expressed with Btr1-like and 122 genes co-expressed with Btr2-like, with 105 genes in common, supporting Btr-like genes involvement in a shared molecular pathway. We hypothesize that the Btr-like genes play a crucial role in pollen development by facilitating the formation of the callose wall around the meiocyte or in the secretion of callase by the tapetum. Our data suggest that Btr genes retained an ancestral function in cell wall modification and gained a new role in grain dispersal due to changes in their spatial expression becoming spike specific after gene duplication.

See https://link.springer.com/article/10.1007/s00122-022-04029-8

Figure 1: A The genetic map of chromosome 3H of cv. Morex (Pseudomolecules V2 annotation). Orange colour indicates sequences showing homology with the Btr1 gene, green colour indicates sequences showing homology with the Btr2 gene. Ψ indicates a pseudogene. B and C Amino acid sequence alignment for copies of the Btr-like and Btr genes on chromosome 3H. (B) BTR1: HORVU.MOREX.r2.3HG0195510, BTR1-LIKE-a: HORVU.MOREX.r2.3HG0195460, BTR1-LIKE-b1: HORVU.MOREX.r2.3HG0195170 and (C) BTR2: NCBI GenBank: KR813335.1 (OUH602), BTR2-LIKE-a: HORVU.MOREX.r2.3HG0195480, BTR2-LIKE-b1: HORVU.MOREX.r2.3HG0195160, BTR2-LIKE-b2: HORVU.MOREX.r2.3HG0195470 (colour figure online)