Research On The Basis And Regulation Mechanism Of Coconut Exocarp Color Formation

Coconut is a perennial tropical woody crop with high economic value.The color of the epicarp is an important quality trait of the coconut.The color of the coconut epicarp is rich and varied.In order to reveal the basis and regulation mechanism of the color formation of coconut epicarps,this study used the exocarps of four different colors of coconuts,brown dwarf,green dwarf,red dwarf,and yellow dwarf as the main experimental materials.Carry out total chlorophyll extraction,flavonoid and carotenoid metabolome and transcriptome analysis;the main research results are as follows:(1)A total of 13 types of carotene and 221 types of flavonoid metabolites were analyzed in the metabolome.Among them,the number of differential metabolites screened in the comparison group of brown dwarf,red dwarf and yellow dwarf with green dwarf coconut were 82,54 and 75 respectively.The number of up-regulated of differential metabolites exceeded 88%,mainly flavonoids,flavonols,flavonoid carbonates and anthocyanins and other important substances in the synthesis of anthocyanins.The content of peony anthocyanin in epicarp of brown dwarf coconut is significantly higher than that of the other three varieties,and pelargonidin is the most abundant in the epicarp of green dwarf coconut.The contents of delphinium glycosides,cyanidin glycosides and pelargonine glycosides in the epicarp of brown dwarf coconut were significantly higher than those of the other three varieties.(2)The main components of carotenoids in the epicarp of four different varieties of coconuts are β-carotene and lutein;the The relative content of α--carotene,α--cryptoxanthin,α--cryptoxanthin,β-carotene,β-cryptoxanthin,γ-carotene and lycopene in the eoicarp of brown dwarf coconut and red dwarf coconut is significantly higher than that of green dwarf and yellow dwarf coconut,while the content the lutein,violaxanthin,neoxanthin and Xanthin in the epicrap of green dwarf coconutof was significantly higher than that of brown dwarf,red dwarf and yellow dwarf.Zeaxanthin was only detected in the epicarp of green dwarf and Yellow Dwarf Coconut;while the content of Chlorophyll in green dwarf Coconut was significantly higher than the other 3 varieties.(3)After bagging of brown dwarf,yellow dwarf,red dwarf and green dwarf coconut fruits,the epicarp color changes from brown,yellow,red and green to milky white or light yellow,and the carotenoid components are significantly reduced;Phytoene was not detected in the epicarp of red dwarf coconut bagged fruits,and the content of zeaxanthin in the epicarp of the four varieties of coconut after bagging was reduced to zero.(4)The results of transcriptome sequencing showed that there were a total of 1835 differentially expressed genes among the varieties.Some differential genes expression were verified by real-time fluorescent quantitative PCR,and the results were basically consistent with the transcriptome results;among them,The ZEP gene involved in zeaxanthin,violaxanthin and neoxanthin,biosynthesis,has the highest expression level in green dwarf coconuts,and the ANS gene in the anthocyanin synthesis pathway has higher expression levels in yellow short,dwarf and green dwarf coconuts.(5)The combined analysis of transcriptome and metabolome data showed that the MYB genes CCG009411.1 and CCG003753.1 are key regulatory genes in the carotenoid biosynthesis pathway in epicarp of coconut;CCG01867.1 and CCG023098.1 genes are key candidate genes that involved in the biosynthesis of cortex cyanidin in the coconut epicarp and CCG000421.1,CCG000515.1,CCG018191.2,CCG0245671,CCG002218.1 are the key regulatory transcription factors in the biosynthesis pathway of malvain in coconut epicarp which may involved in the anthocyanin biosynthesis.