Molecular Mechanism Of Pigment Accumulation In Zucchini With Different Fruit Colors

The zucchini peel presents a variety of colors such as white,light green,dark green,yellow,and orange due to different pigment components and contents,but the specific regulation mechanism of fruit pigment accumulation is still unclear.In this study,the color difference index,pigment content,and carotenoid components in the peels of white,yellow and orange zucchini materials were measured,combined with transcriptomics and carotenoid metabolizing enzyme gene family analysis,and aimed to reveal the molecular mechanism of pigment accumulation in zucchini fruit.The research results obtained are as follows:(1)The dynamic observation and correlation analysis of the color difference index and pigment content of the white,yellow,and orange zucchini peels showed that the color difference index a* value and the color contribution index CCI value can clearly distinguish the peel color.The a* value and CCI value of the white peel(W)fade from the negative value to 0 as the peel green fades,while the a* and CCI values of yellow peel(Y)and orange peel(O)have been positive since the 0th day of pollination,and and gradually increased throughout the development period,and significant differences began to appear at 10 days of pollination..In addition,the content of chlorophyll in W is relatively high.As the development of the peel continues to decrease,the carotenoid content remains low throughout the development period.The chlorophyll content in Y and O has been at a low level,but the carotenoid content continues to increase.At 10 days of pollination,the carotenoid content in yellow peel and orange peel is significantly different.Correlation analysis shows that chlorophyll content and color difference index are negatively correlated,and are strongly correlated with L* and CCI values;carotenoid content and color difference index are both positively correlated,and have a strong correlation with the a*,b*,and CCI values.(2)Carotenoid components were detected in the peels 10 days after pollination.A total of 14 carotenoids were detected in the zucchini peel using LC-MS/MS technology.Among them,11 carotenoids,such as γ-carotene and β-carotene,were detected and accumulated in the three materials.While ε-carotene was only accumulated in Y and O,and lycopene and phytoene were only accumulated in O.Lutein is the main different carotenoid in zucchini peel,accounting for 84.7%(OD,1543.333±127.192 μg·g-1)and 88.25%(YD,509.667±60.358 μg· g-1),75.02%(WD,103.167±3.877 μg·g-1).(3)Transcriptomics analysis revealed that the enzyme genes related to chlorophyll biosynthesis and degradation pathways,carotenoid synthesis pathway in Y and O had relatively high expression levels.The weighted gene co-expression network analysis(WGCNA)was used to divide differentially expressed genes into 12 co-expression modules,among which the blue and green modules were highly correlated with carotenoid and chlorophyll content,respectively.The transcription level of Some hub genes(PIF4,APRR2,b HLH128,ERF4,PSY1,LCYE2,RCCR3)is highly correlated with the pigment content in the peel,which may be responsible for the carotenoids accumulation and Chlorophyll degradation in Y and O.(4)Using bioinformatics methods to identify 48 carotenoid metabolizing enzyme genes in zucchini,and systematically analyze their sequences and evolution characteristics,gene expression patterns,and transcription factor regulation.The results show that the 48 enzyme genes are divided into 11 groups,the functional domains of similar enzyme genes are highly conserved,and only NCED/CCD,PDS/ZDS,LCYE/LCYB gene members have the same functional domains and belong to the same group.These enzyme genes are distributed in regions with higher gene density on 18 chromosomes except LG17 and LG18 chromosomes,and 43 and 47 orthologous genes were found in Chinese pumpkin and Indian pumpkin.Analysis of gene expression patterns showed that multiple key enzyme genes such as GGPPS1,PSY1,LCYE2,etc.play a vital role in tissue specificity and flesh development.The analysis of the cis-acting elements of the promoter indicated that the carotenoid synthase gene may be regulated by multiple types of transcription factors such as MYB,b HLH,b ZIP,and so on.In summary,this study has initially revealed the changes of zucchini peel pigment accumulation,analyzed the peel pigment composition and related gene expression patterns,and explored the potential role of carotene anabolic enzyme genes in growth and fruit quality.This study provide theoretical basis for indepth study of the molecular mechanism of zucchini peel pigment accumulation and creation of new germplasm rich in carotenoids and chlorophyll.