Developmental Changes in Gene Expression Drive Accumulation of Lycopene and β-Carotene in Watermelon

Abstract

<jats:p><jats:italic>Citrullus lanatus</jats:italic> (watermelon) is an excellent daily source of dietary lycopene and β-carotene. To investigate the transcriptional regulation of carotenoid biosynthesis genes relative to lycopene and β-carotene accumulation in watermelon fruit, six watermelon accessions with different flesh colors were examined in this study: white-fleshed PI 459074, pale-yellow-fleshed ‘Cream of Saskatchewan’, light-pink-fleshed PI 482255, orange-yellow-fleshed ‘WM-Clr-1’, and red-fleshed ‘LSW177’ and ‘MSW28’. The expression patterns of eight genes (<jats:italic>PSY1</jats:italic>, <jats:italic>PSY2</jats:italic>, <jats:italic>PDS</jats:italic>, <jats:italic>ZDS</jats:italic>, <jats:italic>CRTISO</jats:italic>, <jats:italic>LCYB</jats:italic>, <jats:italic>NCED1</jats:italic>, and <jats:italic>NCED7</jats:italic>) involved in lycopene and β-carotene biosynthesis and biodegradation were analyzed. The results confirmed the accumulation of large quantities of lycopene in red-fleshed ‘LSW177’ and ‘MSW28’, reflecting the elevated expression of <jats:italic>PSY1</jats:italic> and the low transcriptional expression of <jats:italic>NCED1</jats:italic>. The relative expression levels of <jats:italic>NCED1</jats:italic> likely play an important role in the color development of the light-pink-fleshed PI 482255, whereas the reduced transcriptional expression of <jats:italic>PSY1</jats:italic> and the increased expression of <jats:italic>NCED1</jats:italic> appear to be the main factors contributing to the formation of white flesh in the fruit of PI 459074. Low transcriptional expression of <jats:italic>PSY1</jats:italic> results in the pale-yellow flesh of the ‘Cream of Saskatchewan’ fruit.</jats:p>

Functional Characterization and in Silico Analysis of Phytoene Synthase Family Genes Responsible for Carotenoid Biosynthesis in Watermelon (Citrullus lanatus L.)

“…While both ClPSY1 and ClPSY2 had similar transcript profiles till 18 DAP, the ClPSY1 levels were 3.3-fold higher than that of ClPSY2 at 26 DAP and peaked at 42 DAP, which was consistent with the pattern of lycopene accumulation (Figure 4B). Based on these results and previous reports detailing lack of correlation between the ClPSY2 levels and lycopene content in watermelon of different flesh color [61], we hypothesize that ClPSY1 has a dominant role in the carotenoid biosynthetic pathway during watermelon fruit ripening.…”

“…In contrast, its paralog CmPSY1 is predominantly expressed in the ripe melon fruit [28]. Wang et al [61] analyzed ClPSY2 transcripts in six watermelon cultivars with distinct fruit pigmentation and found that the expression profile of ClPSY2 was not consistent with lycopene accumulation. The red-fleshed MSW28 cultivar had the highest lycopene content, while ClPSY2 displayed lower levels.…”

Fine Mapping of Lycopene Content and Flesh Color Related Gene and Development of Molecular Marker–Assisted Selection for Flesh Color in Watermelon (Citrullus lanatus)

“…This might indicate that the accumulation of lycopene was not dependent on the expression of LCYB . It was also likely that the difference in protein levels or functionality may regulate the color of the fruit (Wang et al, 2016). This seemed contradictory when we combined the results of QTL mapping and transcriptome analysis.…”

The genes crucial to carotenoid metabolism under elevated CO2 levels in carrot (Daucus carota L.)

“…There are usually multiple PSY genes in plants, but only one has been found in Arabidopsis 26 and three in tomato and cassava 27 . Not every PSY gene is related to carotenoid accumulation in fruits, and their expression is specific 28 . In this study, three PSY genes were found, and PSY-1 and PSY-2 were upregulated under CO 2 enrichment.…”