Mapping of quantitative trait loci for lycopene content and fruit traits in Citrullus lanatus

Abstract

Lycopene content is an important factor for determining watermelon fruit quality. However, the low DNA polymorphism among cultivated watermelon (Citrullus lanatus) has hindered the ability to establish high quality genetic maps and study the quantitative trait loci (QTL) controlling the lycopene content trait. In this study, we successfully constructed a genetic map of watermelon to determine lycopene content and other horticultural fruit traits using a F 2 population developed from a cross between the two lines of watermelon LSW-177 and Cream of Saskatchewan. The genetic map contained 16 linkage groups covering a total length of 2,039.5 cM, which included 37 SSRs (Simple Sequence Repeat) and 107 CAPSs (Cleaved Amplified Polymorphic Sequences), with all of the CAPS markers developed from high-throughput re-sequencing of data from this study. Three CAPS markers (WII04E07-33,WII04E07-37,WII04E07-40) caused the F 2 population to perfectly co-segregate for each F 2 population plants. We also obtained 12 QTLs for all of the traits measured. Only one QTL (LCYB4.1) was detected with a high value of trait variation (83.50 %) that related to lycopene content and mapped on Chromosome 4 between CAPS markers WII04E07-33 and WII04E07-40, which could nearly account for all of the differences in lycopene content between the two parental strains. In this study, we highlighted 2,458 CAPS loci that were suitable for primer design with a polymorphism of 48.9 %, which is approximately a 12-fold increase from previous studies. The present map and QTLs will facilitate future studies on determining lycopene content related genes and cloning watermelon genes, while also providing for useful markers for breeding for lycopene content.

Comparative transcriptome analysis of two contrasting watermelon genotypes during fruit development and ripening

“…In a recent study [8], we characterized the carotenoid contents in COS and LSW177, and these two cultivars were selected for further study due to their different lycopene contents and the degree of difference in their mechanisms regulating lycopene accumulation during fruit ripening. A total of 20 cDNA libraries prepared from fruit flesh samples at the four critical ripening stages and one over-ripening stage (with two biological replicates for each stage and watermelon species) were sequenced (described in methods; Fig.…”

“…The continuously low expression level of LCYB and LCYE from the early to the mature stage was likely the main reason that the newly biosynthesized lycopene in LSW177 could not be further catalyzed to synthesize β-carotene or α-carotene and was gradually deposited in the vacuole to form red flesh. In our previous research, the red-flesh trait in the F2 and F3 population from COS × LSW177 was located in LG4; interestingly, LCYB was located between the two cleaved amplified polymorphic sequence (CAPS) markers WII04E07-33 and WII04E07-40, which were tightly linked to the red-flesh trait, with R 2  = 83.5% [8]. In the LCYB -coding/promoter regions, a very small amount of activity of the LCYB enzyme induced by SNPs or INDEL likely results in lycopene accumulation [31–33].…”

“…Approximately 5 g of flesh was used to analyze the lycopene content, as previously published [8]. Every sample was examined using three replicates.…”

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

“…Three grams of homogenized flesh at different fruit stages were used for carotenoid extraction. The carotene extraction method was performed according to Liu et al (2015), with some modifications. The samples were dissolved in the mobile phase [2 methyl alcohol : 5 acetonitrile : 3 dichloromethane (by volume)] and filtered through a 0.22-mm organic nylon filter.…”

“…The lack of a precursor metabolite supply and high transcript levels of NCED result in small quantities of carotenoids in yellow and white fruit. The LCYB gene has been reported as a major quantitative trait locus (QTL) that could increase the lycopene content in watermelon (Liu et al, 2015). Obviously, these studies are not completely consistent regarding how they determined the key genes that controlled lycopene and b-carotene in watermelon.…”