Integrated Transcriptome And Metabolome Analysis Unveils The Mechanism Of Color-transition In Edgeworthia Chrysantha Tepals

Edgeworthia chrysantha Lindl.is a deciduous shrub in the family Thymelaeaceae,endemic to China.It blooms in late winter to early spring,with flowers preceding leaves,and has a long blooming period of up to two months.A head shaped inflorescence consisting of 30 to 50 small flowers that bloom from the inside out,with flowers of different colors on the same inflorescence,making it highly ornamental valuable.Despite its long history of cultivation and wide range of applications,there is a significant lack of theoretical research on E.chrysantha.In this study,the tepals of bud-green stage(SI),full-bloom-yellow stage(S2)and final-bloom-white stage(S3),which are significantly different in flower color,were used as experimental materials.By measuring the changes of their flower color phenotype and pigment content,combined with the qualitative and quantitative analysis of metabolome and the sequencing analysis of transcriptome,the internal regulation mechanism of flower color changes during E.chrysantha flowering was preliminarily clarified,which can provide theoretical basis for genetic improvement of E.chrysantha flower color.The main research findings are as follows:(1)Quantification of the color phenotype trend:The phenotypic parameters of each flower color showed significant differences between the three periods.Except for the gradual increase in the L*value,the a*value,b*value,and chroma C value all showed a trend of first increasing and then decreasing.(2)Correlation analysis of the trend in pigment content changes and identification of key pigments:The content of different pigments showed significant differences in different periods.The content of carotenoids first increased and then sharply decreased,while the content of chlorophyll and flavonoids decreased as the flower developed,but the decline in chlorophyll content was greater.The content of carotenoids showed an extremely significant positive correlation with the b*value and chroma C value,indicating that carotenoids are key pigments in the process of coloration.(3)Identification of key metabolites during flower color changes:Using qualitative and quantitative analysis of the carotenoid metabolic profile,33 carotenoid substances were detected across three periods,with 14 metabolites annotated to the carotenoid biosynthesis pathway.As color change progresses,the content of phytoene continuously increases,while the content of lutein,β-carotene,and α-carotene continuously decreases.Most of the remaining metabolites exhibit an initial increase followed by a decrease.The high levels of lutein and β-carotene in S1 may contribute to the yellow attribute of the flower petals during the budding stage.The types and levels of carotenoids in S2 surpass those in other stages,with the significant increase of key metabolites like antheraxanthin,zeaxanthin,lycopene,and α-cryptoxanthin being responsible for the coloration of flower petals during the blooming period.Except for the colorless lycopene,the levels of all other carotenoids significantly decreased to a very low level in S3,leading to the fading of yellow coloration.(4)Identification of key genes and transcription factors:Transcriptome sequencing analysis was performed on nine samples from three stages,with a total sequence quality of 61.97 G and clean bases greater than 6.5 G for each sample.A total of 153,301 Unigenes were assembled,of which 75447(49.21%)Unigenes were annotated.Carotenoid biosynthesis pathway was significantly enriched in all pairwise comparisons of different stages,and 33 differentially expressed genes were screened out.Most of the synthesis-related genes showed high expression in S1 and S2,with expression trends of PSY,Z-ISO,crtZ,ZEP and other genes showing an initial increase followed by a decrease,with S2 having the highest expression levels,consistent with the changing trend of the b*value and chroma C value.PDS and ZDS were highly expressed in S1.All above play an important role in the synthesis and accumulation of metabolites.While degradation-related genes began to be highly expressed from S2 and reached their peak in S3,with NCED being the main gene responsible for degradation.The overall synthesis intensity of S1 and S2 was greater than that of degradation,leading to a higher accumulation of color metabolites in S2,while the overall degradation intensity of S3 was much greater than that of synthesis,resulting in a rapid decrease in the content of color metabolites.Besides,two C2H2 transcription factors(positive regulation)and one MYB transcription factor(negative regulation)were identified.Analysis of the porphyrin and chlorophyll metabolism pathway indicated that SGR is the key gene responsible for the continuous decrease in chlorophyll content.qRT-PCR validation results were consistent with the transcriptome sequencing data.