Accumulation of carotenoids and expression of carotenoid biosynthesis genes in fruit flesh during fruit development in two Cucurbita maxima inbred lines

Mesocarp color is an important agronomic trait of Cucurbita maxima and is determined mainly by the contents and compositions of the carotenoids.The two inbred lines with significant differences in fruit flesh color were used in the study,the orange’312-1’and white’98-2’.Changes in seven carotenoid contents and compositions in the flesh of fruit produced by inbred lines’312-1’and’98-2’were analyzed during fruit development.The expression of eight key carotenoid biosynthesis genes in the fruit flesh were investigated during five fruit development stage in two inbred lines.As the flesh color intensified,the orange flesh color of’312-1’was determined mainly by the increased contents of lutein,β-carotene and zeaxanthin and the lack of carotenoid accumulation led to the formation of white flesh in’98-2’fruit.The expression of the LCY-e and CHYb genes was significantly stronger in’312-1’than in’98-2’,and their expression was strongly correlated with lutein andβ-carotene contents during fruit development.This study provides a deep understanding of the molecular mechanism of carotenoid biosynthesis in fruit flesh and provides a basis for additional studies on the highly refined improvement of squash quality.

High-density genetic mapping identified a major locus for environmental sex expression in pumpkin(Cucurbita moschata Duch.)

Long-day length and high temperature inhibit sex expression in pumpkin(Cucurbita moschata Duch.),and therefore directly impact the production potential.In this study,female flowering patterns in photoperiod-insensitive(PPIS)and photoperiod-sensitive(PPS)germplasms differed significantly in a moderately long day and high temperature environment.However,both germplasms exhibited a similar response in short day with either low temperature or high temperature environment.Photoperiod sensitivity led to this difference in sex expression between the germplasms.For the traits of 1st female flowering node(FFFN)and number of female flowers(NFF),high-density linkage map construction and quantitative trait locus(QTL)mapping were performed using SLAF-seq technology and 162 F_(2) individuals generated from PPIS and PPS.In total,4655 SLAFs were selected and mapped on 20 linkage groups(LGs).The total map length was 2502.01 cM with an average interval distance of 0.75 cM.Major QTLs for both FFFN and NFF were detected on LG6 with intervals of 7.89 and 17.67 cM and PVE values of 30.5%and 22.9%,respectively.Further analyses of the major locus for FFFN revealed 73 protein-coding genes.Among them,4 were related to sex expression,photoperiod flowering,and hormone response.An InDel(insertion and deletion)marker partially correlated with FFFN of the F_(2) population was also developed.Our study identified the QTL for the sex expression response to environmental factors using the high-density linkage map.The identified candidate genes and markers will provide useful information about the molecular interaction between the environment and sex expression and for marker-assisted selection of pumpkin environment-insensitive resources.