Identification of a member of the catalase multigene family on wheat chromosome 7A associated with flour b* colour and biological significance of allelic variation.

Abstract

Carotenoids (especially lutein) are known to be the pigment source for flour b* colour in bread wheat. Flour b* colour variation is controlled by a quantitative trait locus (QTL) on wheat chromosome 7AL and one gene from the carotenoid pathway, phytoene synthase, was functionally associated with the QTL on 7AL in some, but not all, wheat genotypes. A SNP marker within a sequence similar to catalase (Cat3-A1snp) derived from full-length (FL) cDNA (AK332460), however, was consistently associated with the QTL on 7AL and implicated in regulating hydrogen peroxide (H2O2) to control carotenoid accumulation affecting flour b* colour. The number of catalase genes on chromosome 7AL was investigated in this study to identify which gene may be implicated in flour b* variation and two were identified through interrogation of the draft wheat genome survey sequence consisting of five exons and a further two members having eight exons identified through comparative analysis with the single catalase gene on rice chromosome 6, PCR amplification and sequencing. It was evident that the catalase genes on chromosome 7A had duplicated and diverged during evolution relative to its counterpart on rice chromosome 6. The detection of transcripts in seeds, the co-location with Cat3-A1snp marker and maximised alignment of FL-cDNA (AK332460) with cognate genomic sequence indicated that TaCat3-A1 was the member of the catalase gene family associated with flour b* colour variation. Re-sequencing identified three alleles from three wheat varieties, TaCat3-A1a, TaCat3-A1b and TaCat3-A1c, and their predicted protein identified differences in peroxisomal targeting signal tri-peptide domain in the carboxyl terminal end providing new insights into their potential role in regulating cellular H2O2 that contribute to flour b* colour variation.