Understanding and regulating pre-maturity a-amylase activity in wheat grains to maintain high Hagberg Falling Number (PhD)

Summary

Sector:
Cereals & Oilseeds
Project code:
SR25
Date:
01 October 2009 - 30 September 2012
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£37,500
Total project value:
£105,900
Project leader:
Kirtikumar Ramesh Kondhare

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About this project

Abstract

The occurrence of pre-maturity α-amylase (PMA) in wheat grains is a major problem in the UK and elsewhere. Flour produced from PMA induced grains has poor bread making potential (low Hagberg Falling Number [HFN]). Several factors such as genotype, agronomy and environmental conditions are responsible for PMA induction. Out of which, cool and wet weather around mid-grain development is the major stimulus for PMA induction. This report presents four glasshouse experiments conducted to understand the role of the hormones abscisic acid (ABA) and gibberellins (GAs) in the mechanism of PMA induction. The ultimate aim of this project is to identify ways in which plant breeders can develop varieties with low PMA and more reliable HFN.

The hypothesis studied in this project was that there is a change in ABA and/or GA sensitivity or in their levels in wheat grains during PMA induction by a cool-temperature shock. In situ (Experiment 1) and in vitro (Experiment 3) experiments tested the first part of the hypothesis. These experiments studied ABA and GA sensitivity of intact grains with embryos or detached grains without embryos under cool-temperature shock-inducing and non-inducing conditions. Overall, these two experiments concluded that PMA is related to increased GA sensitivity in the susceptible variety Rialto (Experiments 1 and 3). The change in sensitivity occurs at about 36 day after anthesis (DAA) and is limited to the aleurone (not the embryo) (Experiment 3). There was little evidence for a change in ABA sensitivity (Experiments 1 and 3). In experiment 2, a cool-temperature shock significantly increased GA sensitivity in both Rht-D1a (tall) and Rht-D1b (semi-dwarf)genotypes with or without the 1B1R (wheat-rye) chromosome translocation. These results suggested that the risk of PMA induction is very high and represents a serious problem to wheat breeders and growers.

Experiment 4 tested the second option using an alternative approach. In this experiment, induced grains produced significantly low ABA levels compared to non-induced grains at 29/31 DAA. This offers one possible mechanism through which cool-temperature can alter GA sensitivity. A significant increase in α-amylase in fluridone-treated (ABA biosynthesis inhibitor) grains under non-inducing conditions was associated with a significant increase in GAs. A significant decrease in α-amylase for paclobutrazol-treated (GA biosynthesis inhibitor) grains under inducing conditions was associated with a significant decrease in GAs. These results show that GA levels also play a role in α-amylase formation in developing grains, in addition to GA sensitivity.

The results from this project suggested the strategy to develop a new wheat variety with better bread making quality, which involves three major steps: A. Screening PMA-inducible varieties through the cool-temperature shock screening method, B. Constructing a transgene containing GA hypo-sensitiveness (either through the GID1 [GA] receptor or the DELLA protein) with a promoter, which governs the gene expression specific only in the embryo or the aleurone of developing grains, and transform the transgene into a PMA-inducible variety and, C. Marker selection for GA hypo-sensitivity. Alternative strategy is to look for the available molecular markers (QTL), which govern the GA hypo-sensitivity in wheat genome and use them to develop breeding strategies to improve HFN stability e.g. use of high throughput approaches such as Marker-Assisted Selection and Targeting Induced Local Lesions in Genomes.

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