Understanding the genetic and physiological control of pre-harvest sprouting and pre-maturity amylase in UK wheat
Pre-harvest sprouting (PHS) and Pre-maturity amylase (PMA) are physiological defects in wheat grains that reduce their end-use quality. PHS is the precocious germination of grains before harvest while PMA is the accumulation of α-amylase in grains. Both traits are quantitative in their expression and are strongly influenced by the environment. In this project, I studied six Quantitative Trait Loci (QTL) located on chromosomes 1A, 2D, 3A (2 loci), 4A and 7B, which confer resistance to PHS or PMA in UK wheat varieties. The aims of this project were to validate and characterise the effects of these QTL, as well as to fine-map the QTL with the most significant effect. To achieve these aims, isogenic materials were developed to independently study these QTL effects. Physiological characterisation of these QTL showed that they exert their effects by affecting the dynamic of dormancy loss in grains, albeit at different stages of grain development and maturation. We also show that temperature during grain development and germination affect the expression of these QTL effects. In addition to the characterisation above, I also undertook the fine-mapping and positional cloning of the 4A QTL (named Phs), as this QTL showed the highest effect on PHS resistance of all the QTL studied. I took advantage of recent advances in wheat genomics, high-throughput genotyping and the syntenic relationship between wheat and other grasses, to delimit Phs to a less than 0.2 cM interval. Furthermore, examination of the physical map of this interval identified 17 genes with varied biological functions. High-resolution fine-mapping of the 0.2 cM interval in three independent and diverse populations further delimited Phs to a 10 kb genomic interval. Finally, I report on the comparative sequence analysis around this critical interval, and show the presence of some genomic lesions that could be critical for the Phs effect.
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