Gene expression profiles of seed coats and biochemical properties of seed coats and cotyledons of two field pea (Pisum sativum) cultivars contrasting in green cotyledon bleaching resistance

Visual quality is one of the major factors determining the market value of field pea (Pisum sativum L.). Breeding for improved visual quality of pea seeds is currently a challenging task, mainly because of the complexity and the lack of sound genetic knowledge of the traits. The objectives of this research were to characterize post-harvest cotyledon bleaching resistance in green pea at the biochemical and gene expression levels. Seed coats and cotyledons of two pea cultivars, CDC Striker (bleaching resistant) and Orb (bleaching susceptible) at three developmental stages [14, 21 and 28 days after flowering (DAF)] and following exposure to accelerated bleaching conditions after harvest (0, 3, 6, and 13 days after bleaching (DAB) were evaluated. CDC Striker had a slower rate of chlorophyll degradation in cotyledons, and a higher total carotenoids to chlorophyll ratio in seed coats, than Orb when seed samples were exposed to high intensity light. An oligo-nucleotide microarray (Ps6kOLI1) revealed that gene expression profiles of the CDC Striker and Orb seed coats were significantly different during seed developmental stages. A significant up regulation of genes involved in the production and accumulation of secondary metabolites responsible for antioxidant properties including epiafzelechin, epicatechin, epigallocatechin, kaempferide, kaempferol 3-O-beta-d-sophorotrioside, O-quercetin and rutin, in the seed coats of CDC Striker were observed. Thus, bleaching resistance in field pea could be due to the accumulation of specific carotenoids and phenolic compounds which quench excess light or scavenge free radical singlet oxygen molecules. The candidate genes identified in this project will need to be validated using qPCR to further support their involvement with bleaching resistance before being used for the development of gene specific markers.