Transcriptomic And Metabolomic Analysis Of Anthocyanin Biosynthesis In The Storage Root Of Sweet Potato

Anthocyanins are a subclass of flavonoids with multiple physiological functions.P urple-fleshed sweet potato has enormous anthocyanin reserves which are sources of lower molecular weight antioxidants.These antioxidants offer several health benefits.Hence,purple-fleshed sweet potato is highly preferred as an emerging health food in the wake of growing health consciousness and food security.Therefore understanding the mechanism of anthocyanin biosynthesis and accumulation is imperative for breeding more a nthocyanin-rich sweet potato varieties.In this project,we combined transcriptome and metabolome analysis to study expression patterns of genes in different flesh-colored and metabolite distribution sweet potato to resolve how they regulate anthocyanin biosynthesis and accumulation.K nowledge gained through this project is inherently valuable as it gives insights into the mechanisms underlying the intriguing phenomenon of anthocyanin biosynthesis and accumulation.This will further facilitate the molecular breeding of sweet potato cultivars with superior anthocyanin content.To understand the molecular mechanism of anthocyanin biosynthesis and accumulation,a full transcriptome and metabolome comparison of sweet potato materials with contrasting flesh colors,specifically,Guangshu87（GS87）and Ziluolan（ZLL）was performed.To ascertain whether or not genetic materials are transferred from parents to their offsprings and to futher understand the mechanism of anthocyanin biosynthesis in sweet potato,a transcriptomic study was conducted on the F₁ generation,185-P and its mutant,185-W.NCBI Blastp was used to screen for anthocyanin-related genes and annotate their functions.Further,q RT-PCR analysis was performed to validate the expression patterns of ten randomly selected genes.The transcriptome sequencing data of GS87 and ZLL revealed that 24,388 unigenes were assembled from 61,335,186 high-quality reads.Out of this number,4,469 were differentially expressed genes（DEGs）with 2,532 up-regulated and 1,937 downregulated genes.A total of3,602（80.6%）DEGs were annotated with functions in the non-redundant protein database.Gene Ontology（GO）analysis classified the DEGs into 48 GO terms under cellular components,biological processes,and molecular function categories.From the transcriptome sequencing data of 185-P and 185-W,a total of 239,415,012 high-quality reads were assembled into 27,889unigenes.264 differentially expressed genes（DEGs）were detected with 100 upregulated genes and 164 downregulated genes,of which 255（96.6%）were annotated with putative functions in public databases.GO classifications categorized the DEGs into 36 GO terms under cellular components,biological processes,and molecular function categories.From the GO analysis,19terms under the biological processes（ten terms）and molecular function（nine terms）categories were related to anthocyanin biosynthesis among the two DEG groups（GS87 vs Z LL and 185-P vs 185-W）.O ur results indicated that the flavonoid and phenylpropanoid biosynthesis pathways were the main signaling pathways for anthocyanin biosynthesis.Nearly all pathway genes linked to anthocyanin biosynthesis including ANS,DFR,CHS,F3H,CHI,F3H,and 3GT were identified except F3′5′H,which is attributed to the loss of this gene from the genus Ipomoea.Sequence analysis using NCBI Blastp showed that these genes were homologous to corresponding genes in other plant such as Arabidopsis,petunia,rice,and some Ipomoea spp.such as I.nil,I.purpurea and I.triloba.Furthermore,the b HLH and MYB TFs of the MBW complex were identified as the main TFs that regulate anthocyanin biosynthesis.Notably,almost all TF and structural genes linked to anthocyanin biosynthesis were significantly up-regulated.Also,qRT-PCR analysis to validate the expression patterns of ten randomly selected genes was performed.The results were in agreement with the transcriptome sequencing data which confirmed the high reliability of ther sequencing data.All four anthocyanin-related genes were significantly upregulated in the purple varieties,suggesting their role in anthocyanin biosynthesis.From the metabolic profiling,a total of 122 metabolites were identified,of which 53 metabolites（6 upregulated and 47 downregulated）exhibited differential expression patterns between the two cultivars（GS87 and ZLL）.Principal component and clustering analyses revealed distinct metabolic profiles between the different cultivars with the metabolites mostly enriched to the flavonoid and anthocyanin biosynthesis pathways.Anthocyanins and flavonoids appeared as the most prominent metabolites and peonidin,cyanidin,petunidin,and delphinidin were the most prominent metabolites in the anthocyanin biosynthesis pathway.This suggests that these metabolites might contribute to the observed phenotypic differences in flesh color.From our findings,we infer that the differential expression of structural gene s and TFs related to anthocyanin biosynthesis resulted to the altered metabolic profiles among the different varieties.This accounted for the observed phenotypic difference in flesh color.We also speculate that the b HLH and MYB TFs are the key genes involved in anthocyanin biosynthesis in sweet potato.