The Study On Response Characteristics And Regulatory Mechanism Of Metabolites During Morphogenesis In Catharanthus Roseus Seedlings

Throughout the life span of plants,the seedling morphogenesis after seed germination is essential for plant growth and development.In order to understand this process,studies were mainly devoted to identify key regulatory factors and uncover the underlying mechanism.Metabolites play a key role in plant growth and development,but the synthesis,accumulation and function of metabolites during seedling morphogenesis were rarely reported.Madagascar periwinkle(Catharanthus roseus(L.)G.Don)is one of the most widely-known anticancer plant medicinal sources,in addition to the specific accumulation of Terpenoid Indole Alkaloids(TIAs),it can also synthesize other metabolites through multiple complex metabolic pathways,such as phenolic compounds.Therefore,in this study,the response characteristics of metabolites in skoto-and photo-morphogenesis of C.roseus seedlings were compared by using the omics methods,and the regulatory mechanism of metabolites biosynthesis was further elaborated.Our findings were mainly including:(1)The morphogenesis of C.roseus seedlings under both light and dark conditions was compared.The skoto-morphogenesis was characterized by the continuous elongation of hypocotyl,the closure of apical hook,as well as the closed and etiolated cotyledon.The content of carbohydrates accumulated significantly while the photosynthetic pigments did not change;On the contrary,photo-morphogenesis developed into inhibition of hypocotyl growth,opening of the apical hook,greening and expansion of cotyledon,and development of root system,accompanied by the continuous accumulation of photosynthetic pigments and acids.(2)In whole seedling,the global content of phenolic compounds mainly concentrated during the period of apical hook opening.By comparing the content of phenolic compounds in the hypocotyl,it was found that the content of C6C3-type cinnamic acid derivatives and the enzymatic activity of C4 H were increased significantly upon light condition.However,in the dark,C6C3C6-type flavonols were accumulated markedly in the inner side of the apical hook while were barely detectable in the hypocotyl.Only a slight accumulation in the hypocotyl was observed in the de-etiolated seedlings.This result implied that the significant accumulation of flavonol in the inner side of apical hook in dark of C.roseus seedling may be related to the polar transport of auxin.(3)By comparing the content of phenolic compounds in different tissues,it was found that the accumulation of these metabolites in cotyledons was higher than that in roots or hypocotyls.In the photo-morphogenesis of seedling,the most significant phenotypic characteristics of cotyledons are cotyledon greening and expansion process.During this stage of development,a large amount of Protochlorophyllides and ROS accumulated in the etiolated cotyledon,while the significant accumulation of C6C3C6-type flavonoids in the de-etiolated and greening cotyledon,which inhibited the content of ROS in the cotyledon and thus to protect the seedling to survive.(4)Transcriptome analysis identified a series of enzyme genes related to the phenolic metabolic pathway in C.roseus seedling,which were significantly up-regulated under light condition.In addition,through comparative analysis with Arabidopsis,it was found that some potential transcription factors significantly induced upon light exposure,such as Cr HY5(CRO＿T122304),CRO＿T137938,CRO＿T104753,CRO＿T107249,etc.,may be directly or indirectly involved in the biosynthesis and regulation of flavonoids in C.roseus.This mining analysis provides new insights into the regulation and potential roles of flavonoids in the cotyledon greening of C.roseus seedling.In conclusion,this study is the first report to systematically and comprehensively compare the metabolic response patterns of primary metabolites and phenolic compounds between skotoand photo-morphogenesis in C.roseus seedling,and discover several key candidate factors which are involved in the biosynthesis and regulation of metabolites.This study also provides a targeted reference for the distribution patterns of other metabolites during seedling morphogenesis,further advance our understanding of the metabolic response and biological functions of metabolites during seedling development,and offer a theoretical basis for the future studies on their potential regulatory mechanisms.