Developmental Changes In Gene Expression Drive Accumulation Of Lycopene And ?-carotene In Watermelon

Watermelon(Citrullus lanatus)is a preferred vegetable or fruit in summer which is famous for cool and sweet taste. Watermelon is a rich source of carotenoid and is regarded as a function food recently. Red-fleshed watermelon contains the mostant abundant amount of lycopene and has attracted much attention in epidemiological and nutritional studies. Pathology studies have shown that increased lycopene intake reduces the risk of cancers and resistance to aging. As the most efficient dietary precursor of vitamin A, ?-carotene is also an essential nutrient for humans and animals. China is the largest consumer of watermelon production and consumption all over the world, in recent years, watermelon breeding in China is mainly in disease resistance, stress tolerance, high yield, good quality and so on. In order to meet the needs of consumers for functional food, the cultivation of watermelon varieties with high lycopene and ?-carotene is an important target of watermelon functional breeding. Getting to know the regulation mechanism of lycopene and ?-carotene in the metabolic pathway is the basis of the functional breeding of watermelon.To investigate the transcriptional regulation of carotenoid biosynthesis genes in relation to lycopene and ?-carotene accumulation in watermelon fruit, seven different fleshed watermelon accessions were examined in the present study: white-fleshed PI 459074, pale yellow-fleshed Cream of Saskatchewan, light-pink-fleshed PI 482255, orange-yellow-fleshed WM-Clr-2, red-fleshed LSW177, PI 179881 and MSW28. The expression patterns of eight genes(PSY1, PSY2, PDS, ZDS, CRTISO, LCYB, NCED1 and NCED7) involved in lycopene and ?-carotene biosynthesis and biodegradation were analyzed.(1) No lycopene or ?-carotene content was detected in the white-fleshed PI 459074 and light-yellow-fleshed Cream of Saskatchew; Lycopene content in the light-pink-fleshed PI 482255 at 56 DAP was approximately one-third or a quarter of red fleshed LSW177, PI 179881 and MSW28. Lycopene and ?-carotene content also varied in LSW177, PI 179881 and MSW28 ranging from MSW28 > PI 179881 > LSW177.(2) Distinct orange-yellow color in WM-Clr-2 did not reflect ?-carotene accumulation, there were other pigment that make the flesh orange yellow.(3) PSY1 and NCED1 play an important role in the color formation of watermelon pulp. The decreased transcriptional expression level of PSY1 and the increased expression level of NCED1 were the key factors contributing to the formation of white flesh ed fruit. Low transcriptional expression of the PSY1 leaded to the pale yellow-fleshed watermelon.The results confirmed that a large quantity of lycopene accumulated in red-fleshed watermelon, reflecting the elevated expression of the PSY1 and the low transcriptional expression of the NCED1. The high expression level of of NCED1 played an important role in light-pink flesh color development.