Genome-wide Identification And Functional Analysis Of The Melatonin COMT Gene Family In Tea Plan

Tea plant(Camellia sinensis)is an important woody economic crop in China.Environmental stresses such as drought,salt,high temperature and low temperature stress seriously affect the growth and development of tea plants,and the yield and quality of tea products.Melatonin plays an important role in plant growth and stress response.Caffeic acid O-methyltransferase(COMT)is a key enzyme involved in plant melatonin biosynthesis.However,the molecular mechanism of COMT involved in the regulation of melatonin biosynthesis in tea plants is still unclear.In this study,a total of25 CsCOMT genes were screened and identified from the tea plant genome using bioinformatics techniques.The phylogenetic relationship,chromosome localization,gene structure,promoter cis-acting elements and genomic codon preference of CsCOMT gene family members were analyzed.The protein structure(such as protein conserved motifs,signal peptide prediction,spatial structure characteristics,etc.),gene methylation sites,and protein phosphorylation sites of CsCOMT family members were also analyzed.This information provides important clues for further study of the biological functions of CsCOMT gene family members.In addition,the expression patterns of CsCOMT in different tissues and organs of tea plant and in response to hormones and abiotic stresses were analyzed by transcriptome data analysis and q RTPCR verification.Using VIGS gene silencing technology and HPLC analysis technology,it was found that silencing of CsCOMT19 resulted in a significant decrease in melatonin content in tea plants,indicating that CsCOMT19 may play an important role in melatonin biosynthesis in tea plants.These results provide important information for in-depth analysis of the molecular mechanism of CsCOMT involved in melatonin biosynthesis in tea plants,and also provide a reliable theoretical basis for breeding excellent tea varieties.The main results are as follows:(1)A total of 25 CsCOMT genes were screened and identified from the tea plant genome through bioinformatics analysis.These CsCOMT gene family members were divided into three subfamilies by evolutionary relationship analysis,and the same subfamily members had similar gene structures.The CsCOMT gene promoters mainly contain cis-acting elements related to plant growth and development,light response,stress response and hormone response.(2)Bioinformatics analysis showed that CsCOMT family members had similar protein conserved motifs and secondary and tertiary structures,and all members had no signal peptide sequence in their protein sequences.The phosphorylation sites of CsCOMT protein are mainly located on serine and threonine residues,and a few members have methylation modification sites and Cp G islands.There are proteinprotein interactions between CsCOMT4,CsCOMT5,CsCOMT6,CsCOMT9,CsCOMT17,CsCOMT18,CsCOMT19 and CsCOMT25.(3)The expression patterns of CsCOMT gene family members in different tissues of tea plant are different.The expression levels of CsCOMT3,CsCOMT11,CsCOMT19 and CsCOMT25 were relatively high in eight tea plant tissues.The expression levels of CsCOMT6,CsCOMT7,CsCOMT12 and CsCOMT24 were relatively high in at least five tissues.CsCOMT20 was only highly expressed in flowers.The expression levels of CsCOMT1,CsCOMT2,CsCOMT4,CsCOMT9,CsCOMT17 and CsCOMT18 were relatively high only in roots.(4)The expression patterns of CsCOMT gene family members in response to hormones and abiotic stresses were different.Among them,The expression levels of CsCOMT7,CsCOMT10 and CsCOMT24 were significantly decreased after methyl jasmonate treatment for 12 h and 24 h,and the expression of CsCOMT18 was upregulated after methyl jasmonate treatment for 48 h.The expression level of CsCOMT6 decreased under salt stress,but the expression levels of CsCOMT13 and CsCOMT20 increased at 24 h and 48 h under salt stress.Drought treatment decreased the expression level of CsCOMT6 and increased the expression level of CsCOMT25.These results indicate that the above CsCOMT genes may be involved in the regulation of tea plant response to hormone and abiotic stress.(5)Silencing of CsCOMT19 gene by VIGS technology resulted in a significant decrease in melatonin content in tea plants,indicating that CsCOMT19 plays an important role in melatonin biosynthesis in tea plants.