Abstract
BackgroundAlthough starch consists of large macromolecules composed of glucose units linked by α-1,4-glycosidic linkages with α-1,6-glycosidic branchpoints, variation in starch structural and functional properties is found both within and between species. Interest in starch genetics is based on the importance of starch in food and industrial processes, with the potential of genetics to provide novel starches. The starch metabolic pathway is complex but has been characterized in diverse plant species, including pea.ResultsTo understand how allelic variation in the pea starch metabolic pathway affects starch structure and percent amylose, partial sequences of 25 candidate genes were characterized for polymorphisms using a panel of 92 diverse pea lines. Variation in the percent amylose composition of extracted seed starch and (amylopectin) chain length distribution, one measure of starch structure, were characterized for these lines. Association mapping was undertaken to identify polymorphisms associated with the variation in starch chain length distribution and percent amylose, using a mixed linear model that incorporated population structure and kinship. Associations were found for polymorphisms in seven candidate genes plus Mendel’s r locus (which conditions the round versus wrinkled seed phenotype). The genes with associated polymorphisms are involved in the substrate supply, chain elongation and branching stages of the pea carbohydrate and starch metabolic pathways.ConclusionsThe association of polymorphisms in carbohydrate and starch metabolic genes with variation in amylopectin chain length distribution and percent amylose may help to guide manipulation of pea seed starch structural and functional properties through plant breeding.
Highlights
Starch consists of large macromolecules composed of glucose units linked by α-1,4glycosidic linkages with α-1,6-glycosidic branchpoints, variation in starch structural and functional properties is found both within and between species
We have shown that allelic variation in pea starch pathway candidate genes can have a measurable effect on amylopectin chain length distribution (CLD)
We identified polymorphisms in eight genes from the pea seed carbohydrate and starch metabolic pathway as having significant association (FDR ≤ 0.05 or false discovery rate (FDR) ≤ 0.10) with variation in debranched starch CLD, and two genes (r locus and UDP-glucose pyrophosphorylase (UGPase)) as having significant association with variation in %amylose
Summary
Starch consists of large macromolecules composed of glucose units linked by α-1,4glycosidic linkages with α-1,6-glycosidic branchpoints, variation in starch structural and functional properties is found both within and between species. The starch metabolic pathway is complex but has been characterized in diverse plant species, including pea. The pulses include economically important species such as pea (Pisum sativum L.), chickpea (Cicer arietinum L.), common bean (Phaseolus vulgaris) and lentil (Lens culinaris Medik.). The branching patterns of amylopectin have been described in terms of A, B and C chains. C chains contain the only reducing end in intact amylopectin and provide the central chain from which B chains branch via α-1,6-glycosidic branches. Starch molecules pack together to form a semi-crystalline structure that is based on the organization of double helices from amylopectin short chains into crystalline lamellae. The crystalline structure of pea starch has been described as a C-form starch, consisting of both A- and B-types [5]
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