Studies of genetic diversity in wild and cultivated barley and wheat

Abstract

I am presenting three first author research publications in my PhD thesis. Copies of my manuscripts in their published form are preceded by a Statement (part iii) that explores the scientific information at a more detailed and advanced level, summarizes the aims and achievements of my work in the light of current knowledge, incorporates the reviewers comments and discusses my contribution to the field. I studied advanced genetic implications of the process of domestication: the nature and consequences of selective pressures acting on the barley crop in prehistoric agriculture as well as molecular differences within highly similar wheat species to enable reassessment of their identity, phylogenetic affinity and the composition of the Neolithic crop package. The first two papers investigated the molecular patterns of traits assumed to have been targeted during selection for domestication in barley. They report on two phenotypic traits, water utilization and growth vigour, as potentially novel traits targetted during the selection for domestication. Molecular analysis of the sequence diversity of a cytokinin dehydrogenase gene CKX2.1, associated with water utilization, and a wall-associated kinase gene WAK1, involved in root proliferation, in an extensive set of wild barley accessions and historical barley domesticates, highlights the possibility that these genes evolved under selection for domestication and are candidates for genes controlling these phenotypic traits. The observed extreme changes occurred within the coding region of the CKX2.1 gene and within WAK1 cis-regulatory sequences. The absence of CKX2.1 haplotype 3 in landraces compared to wild accessions raised the possibility that selection for domestication was accompanied by water utilization changes imposed by husbandry techniques and that this physiological adaptation to cultivation practices is likely to be a component of the domestication syndrome. Fixation of SNPs within the WAK1 promoter in landraces supports the proposed scenario that our ancestors selected for the overall growth vigour of the plant rather than directly for seed size and proposes plant vigour as a conceivable component of the domestication suite. The third paper is on the molecular identification of hulled, tetraploid wheat species. It describes first, a straightforward and unambiguous PCR test directed at the wheat B and G genome-specific Ppd-1 gene that I have developed in order to distinguish between dicoccoides-dicoccum group, (Turgidum/emmer wheats, AuAuBB) and araraticum-timopheevii group (Timopheevii wheats, AtAtGG), for which morphological misidentification occurs. The test revealed the morphologically misclassified wheat accessions and proved consistent with the results of whole-genome analysis. The discriminatory test for the B and G genomes not only allows fast and correct classification of extant groups, which is a prerequisite for inferring accurate phylogenetic relationships, but it is also suitable for ancient DNA (aDNA) to establish which tetraploid wheat group the archaeological, extinct today, so-called New Glume Wheat, NGW, belongs to.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester