UC Davis

Phytoene synthase (PSY) catalyzes a key reaction in the biosynthesis of carotenoids, which are major contributors of grain yellow pigment content (GYPC) in wheat (Triticum spp.). Although quantitative trait loci (QTL) for GYPC have been linked to PSY1 homoeologs in tetraploid and hexaploid wheat, the underlying molecular and biochemical mechanisms for such associations are not well understood. Functional characterization of wheat PSY1 homoeologs indicated that variations in PSY1 homoeolog enzyme activities did not correspond to different levels of GYPC in the wild-type tetraploid and hexaploid wheat genotypes analyzed. However, a correlation between PSY1 homoeolog expression and carotenoid accumulation in grain endosperm was evident, suggesting that GYPC is at least partially modulated by transcriptional regulation of PSY1 homoeologs in wheat grains. Further promoter analysis of PSY-A1 homoeologs with diverse expression profiles in three wheat genotypes revealed not only potential motifs for light and hormonal responses but also new candidate cis-regulatory elements. Overall, the knowledge on the association of PSY1 homoeolog expression and GYPC can be directly applied to breeding tetraploid and hexaploid wheat varieties with desirable carotenoid levels.