| Dendrobium is the second largest genus in Orchidaceae with high ornamental value,which is a primary source for flower germplasm but lacks varieties with pure bright yellow color and long flower longevity.The native species D.densiflorum possesses pure bright yellow flower while its anthesis lasts only 5-6 days from full bloom to decay.This study aims to explore the relationship between the formation of bright yellow color and the blooming period length,D.densiflorum was as the object,and determined the main color-forming substances of flower and the main phytohormones related to flower senescence through metabolomics.Flowers in different development stages and different parts of D.densiflorum were conduct transcriptome sequencing and metabolomic analysis.In addition,q RT-PCR technology was used to verify the expression patterns of significant differential gene synthesis pathways in D densiflorum.Based on these results,the correlation between flower color and extremely short flower longevity of D.densiflorum were analyzed.The main research results are as follows:(1)The metabolomic analysis results of the whole flowers in full bloom suggested the content of lutein is extremely high,it implied the lutein was the main metabolite of flower color.Through the metabolome analysis of abscisic acid and ethylene in D.densiflorum,which mainly related to plant senescence,it found that the content of ethylene is generally higher than that of abscisic acid.The content of ethylene increased as the content of abscisic acid reduced.An inverse correlation may occur that the higher the ethylene content is,the lower the abscisic acid content.The relationship between them may be antagonistic to each other.(2)The transcriptome sequencing of different flower parts of D.densiflorum in different stages were carried out,a total of 253.88 Gb clean data was obtained,110,775 Unigenes were assembled,genes functional annotation were performed.Significant differentially expressed genes were screened by transcriptome,Combined with the results of functional enrichment analysis and metabolome analysis,14 genes related to carotenoid synthesis were selected,including PSY,PDS,ZDS and etc.The biosynthesis and metabolism pathway of carotenoids in D.densiflorum was mapped based on the results.(3)The q RT-PCR was conducted to verify 14 genes relating to carotenoid synthesis.The results suggested that PSY gene was mainly expressed in the translucent,semi-anthesis and full bloom stages of flower growth,LCYE and CYP97 A genes were continually expressed from bud to full bloom stage.The expression of PDS,ZDS,CRTISO and ZISO genes boosted rapidly during the blooming of D.densiflorum,and began to decline in the decay stage.The expression levels of LCYB,BCH,and VDE are quite high when BCH was present in the blooming stage of flowers,which related to the synthesis of zeaxanthin and antheraxanthin.The NCEDs genes expressed in various flower parts during the entire flowering period and reaches the peak in the decay period of labial petals and sepals.(4)The genes related to ethylene and abscisic acid synthesis were identified based the whole genome of D.chrysotoxum.Combining with the transcriptome and metabolome of D.densiflorum on the biosynthesis and regulatory network of carotenoids,ethylene and abscisic acid,found that a small amount of abscisic acid was cleaved due to the appearing of small amount of zeaxanthin,while a small amount of abscisic acid led to the production of more ethylene.Therefore,the process of flower color formation may have justified the short flowering period of D.densiflorum where inverse correlation between ethylene and abscisic acid played a part.In this study,the molecular mechanism of D.densiflorum flower color formation was analyzed,and the key enzyme genes involved in carotenoid synthesis in flower color of D.densiflorum were screened and verified by experiments through metabolomics,transcriptome analysis and q RT-PCR.Combined with transcriptome and metabolome,the correlation of flower color formation and flower longevity was preliminarily explored.These results could provide theoretical basis for improving Dendrobium breeding. |
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