Deciphering the molecular mechanisms controlling grain length and width in polyploid wheat

Brinton, Jemima (2017) Deciphering the molecular mechanisms controlling grain length and width in polyploid wheat. Doctoral thesis, University of East Anglia.

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There is an urgent need to increase crop yields to address food insecurity. Grain weight, determined
by grain length and width, is an important component of final grain yield. However, our
understanding of the mechanisms that control grain weight in polyploid wheat is limited. The
overall aim of this thesis was to understand the mechanisms that control grain length and width in
hexaploid wheat through the characterisation of two previously identified grain weight quantitative
trait loci (QTL) on chromosomes 5A and 6A.
Using near isogenic lines (NILs) we found that the 5A and 6A QTL act through different
mechanisms to increase grain weight. The 5A QTL acts post-fertilisation, primarily to increase
grain length (4.0%) through increased pericarp cell size. The 5A QTL also has a pleiotropic effect
on grain width (1.5%) during late grain development. The 6A QTL acts during very early grain
development, perhaps pre-fertilisation, and specifically increases final grain width (2.3%).
Fine-mapping reduced the QTL mapping intervals and revealed complex underlying genetic
architectures. The 6A QTL mapped to a large linkage block in the centromeric region of
chromosome 6A containing the known grain size gene, TaGW2_A, although we provide evidence
to suggest that this is not the causal gene underlying the 6A QTL. Fine-mapping of the 5A QTL
suggests that two tightly linked genes with an additive effect on grain length underlie the locus. A
haplotype analysis suggests that the 5A QTL is not fixed in UK germplasm.
The corresponding physical intervals for both the 6A and 5A QTL remain large and contain several
hundred genes, making speculation on candidates for the causal genes difficult. A transcriptomics
study with the 5A NILs provided insight into the genes and pathways that are differentially
regulated and hence may play a role in controlling the differences in grain weight.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Jackie Webb
Date Deposited: 03 May 2018 13:54
Last Modified: 31 Jan 2019 01:38


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