A Preliminary Study On The Character Of Transparent Gill Cap Of Pterophyllum Scalare

Pterophyllum scalare is a popular ornamental fish species among the people,and has the reputation of "queen of ornamental fish".Studying the mechanism of character formation of angelfish is beneficial to the cultivation of angelfish,thus improving its economic value.In the process of practice,we found that the gill cover of angelfish is transparent and opaque.Related studies suggest that the formation of fish transparency is due to the hypoplasia of guanine and melanocytes.In order to explain the formation of transparent operculum.We launched relevant experiments to explore this.The results of transcriptome differential expression of OGC and TGC showed that3636 genes were significantly differentially expressed in OGC and TGC,of which 857 genes were significantly overexpressed in OGC and 2779 genes were significantly overexpressed in OGC.Among the differentially expressed genes,three genes that were significantly low expressed in TGC and associated with the guanine pathway were screened,namely gda,prtfdc1,and gng5.Among them,gda is related to the process of guanine catabolism;PRtfdc1 is related to the activity of guanine phosphate ribose transferase;Gng5 is associated with guanine nucleotide binding protein G.The ROC curve analysis results showed that the predictive efficacy of the three genes for TGC and OGC was 0.944,1,1,respectively,indicating that the three genes can serve as biomarkers significantly correlated with the phenotype of OGC and TGC.In order to search for biomarkers related to transparency traits,metabolomic analysis was conducted on TGC and OGC.154 significantly different metabolites were screened,of which 52 were significantly up-regulated and 102 were significantly down-regulated by OGC compared with TGC.The results of KEGG enrichment pathway analysis of different metabolites showed that the significantly different metabolites screened were mainly concentrated in the four pathways of purine metabolism,glycosylphosphatidylinositol(GPI)-anchor biosynthesis,nucleotide metabolism and ABC transporters.Among the first four metabolic pathways in which KEGG was significantly enriched,guanine,adenine,adenosine,inosine and guanosine in OGC group were higher than those in TGC group,while deoxyguanosine and deoxynucleoside were lower than those in TGC group.We screened out the top three metabolites with VIP value from 154 genes,including inosine 5 ’-phosphate,L-theanine and sulfocholic acid.We integrate AUC and VIP＿value,P＿Value,FC value,six metabolites were screened out,and ROC analysis was performed to test their prediction performance.The six metabolites are inosine 5 ’-phosphate;Sulfocholic Acid;Glucose aspartate;2E-2-butylidene-4-hydroxy-5-methyl-3(2H)-furanone((2E)-2-butylidene-4-hydroxy-5-methyl-3(2H)-furanone);L-Theanine;N-[4-(4-methyl-6-oxy-4,5-dihydro-1H-pyridazin-3-yl)phenyl] acetamide.According to ROC analysis,these six metabolites have good prediction function,which may be related to the formation of transparent gill cap of angelfish.In order to explore the genetic rules of the transparent gill cap trait in the fairy fish,a hybridization experiment was designed to observe the segregation of F1 traits.Four groups were designed,with a total of 12 full sibling families.They are transparent X transparent,opaque X opaque,transparent(♀)X opaque(♂),opaque(♀)X transparent(♂).The results are as follows: 1)All F1 offspring from the three families of transparent X transparent have transparent cheek cap traits.2)There are two types of F1 offspring traits in the three families of opaque X opaque.One is all opaque gill cap traits,and the other is trait segregation.The trait segregation ratio between opaque gill cap and transparent gill cap is 3:1.3)The F1 progeny traits of 6 families with transparent and opaque reciprocal crosses showed 2 traits,one being all opaque cheek cap traits,and the other being a 1:1 separation ratio between opaque cheek cap and transparent cheek cap traits.The segregation ratio of F1 offspring traits in fairy fish conforms to Mendelian genetic law.It is inferred that the transparent gill cap trait is invisible,while the opaque gill cap trait is dominant.And it is controlled by an allele.Through a series of experiments,in order to explore the cause of formation and genetic law of the transparent gill cap character of angelfish,four differential genes related to guanine were found through transcriptome analysis,and their phenotype-related prediction performance was demonstrated.The metabolic pathway of four different metabolites including purine metabolism was found through metabolomic analysis.It can be concluded that the formation of transparent gill cap of angelfish is related to the low expression of purine.Through the hybridization experiment,we found the genetic law of the characters of fairy and transparent gill cap.This study enriches the related research on the body color of angelfish,and can provide reference for further research on the transparency of fish.It can also provide relevant theoretical guidance for the actual production and breeding of Pterophyllum scalare.