Abstract
Key messageAssociation analysis resulted in the identification of specific StGWD alleles causing either an increase or decrease in starch phosphate content which was verified in diploid and tetraploid potato mapping populations.Potatoes are grown for various purposes like French fries, table potatoes, crisps and for their starch. One of the most important aspects of potato starch is that it contains a high amount of phosphate ester groups which are considered to be important for providing improved functionalization after derivatization processes. Little is known about the variation in phosphate content as such in different potato varieties and thus we studied the genetic diversity for this trait. From other studies it was clear that the phosphate content is controlled by a quantitative trait locus (QTL) underlying the candidate gene α-Glucan Water Dikinase (StGWD) on chromosome 5. We performed direct amplicon sequencing of this gene by Sanger sequencing. Sequences of two StGWD amplicons from a global collection of 398 commercial cultivars and progenitor lines were used to identify 16 different haplotypes. By assigning tag SNPs to these haplotypes, each of the four alleles present in a cultivar could be deduced and linked to a phosphate content. A high value for intra-individual heterozygosity was observed (Ho = 0.765). The average number of different haplotypes per individual (Ai) was 3.1. Pedigree analysis confirmed that the haplotypes are identical-by-descent (IBD) and offered insight in the breeding history of elite potato germplasm. Haplotypes originating from introgression of wild potato accessions carrying resistance genes could be traced. Furthermore, association analysis resulted in the identification of specific StGWD alleles causing either an increase or decrease in starch phosphate content varying from 12 nmol PO4/mg starch to 38 nmol PO4/mg starch. These allele effects were verified in diploid and tetraploid mapping populations and offer possibilities to breed and select for this trait.
Highlights
Potato is a healthy and nutritious part of the average Western human diet, contributing carbohydrates and important amino acids and vitamins
Phosphate groups are found attached to amylopectin chains at both C-3 and C-6 positions of the glucose residue (Bay-Smidt et al 1994; Hizukuri et al 1970; Sonnewald and Kossmann 2013)
In this paper we investigate whether the collective information of quantitatively scored SNPs would enable us to deduce the composition of GWD haplotypes in individual tetraploid potato cultivars
Summary
Potato is a healthy and nutritious part of the average Western human diet, contributing carbohydrates and important amino acids and vitamins. The most promising one is Glucan Water Dikinase (GWD1 or StGWD), a gene first described as the R-locus in potato (Lorberth et al 1998) This single copy gene is a key enzyme in starch breakdown (EC 2.7.9.4) and catalyzes the transfer of phosphate to the C-6 position of glucosyl residues of the amylopectin fraction (Ritte et al 2006; Zeeman et al 2007). Breeding for a further increase of the phosphate content in potato starch on the other hand is highly desirable because a high natural degree of phosphorylation could lead to a higher substitution degree making chemical modification processes more efficient and potentially more environmentally friendly
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