Transcriptomic Analysis Reveals Key Genes Related to Betalain Biosynthesis in Pulp Coloration of Hylocereus polyrhizus

Abstract

Betalains have high nutritional value and bioactivities. Red pulp pitaya (Hylocereus polyrhizus) is the only fruit containing abundant betalains for consumer. However, no information is available about genes involved in betalain biosynthesis in H. polyrhizus. Herein, two cDNA libraries of pitaya pulps with two different coloration stages (white and red pulp stages) of Guanhuahong (H. polyrhizus) were constructed. A total of about 12 Gb raw RNA-Seq data was generated and was de novo assembled into 122,677 transcripts with an average length of 1183 bp and an N50 value of 2008. Approximately 99.99% of all transcripts were annotated based on seven public databases. A total of 8871 transcripts were significantly regulated. Thirty-three candidate transcripts related to betalain biosynthesis were obtained from the transcriptome data. Transcripts encoding enzymes involved in betalain biosynthesis were analyzed using RT-qPCR at the whole pulp coloration stages of H. polyrhizus (7-1) and H. undatus (132-4). Nine key transcripts of betalain biosynthesis were identified. They were assigned to four kinds of genes in betalain biosynthetic pathway, including tyrosinase, 4, 5-DOPA dioxygenase extradiol, cytochrome P450 and glucosyltransferase. Ultimately, a preliminary betalain biosynthetic pathway for pitaya was proposed based on betalain analyses, gene expression profiles and published documents.

Proteomic Analysis of Hylocereus polyrhizus Reveals Metabolic Pathway Changes

“…These results were consistent with our previous findings from transcriptomic analysis that these enzymes might be involved in betalain biosynthesis in H. polyrhizus [68]. …”

“…More interestingly, five proteins, namely comp37375_c0_seq2_4 and comp37375_c0_seq1_4 (polyphenol oxidase), comp37692_c0_ seq1_7 (4, 5-DOPA dioxygenase extradiol-like), comp16058_c0_seq1_4 (CYP76AD3), and comp26435_c0_seq1_2 (Aromatic- l -amino-acid decarboxylase), were identified as some of the key enzymes in the betalain biosynthesis pathway (Table 2). Not surprisingly, the transcriptional levels of these proteins were increasing with the progression of the betalain formation in the pitaya fruit as revealed in our previous study [68]. …”

“…A total of about 12 Gb raw RNA-Seq data were generated and de novo assembled into 122,677 transcripts, of which 122,668 were annotated [68]. Differentially expressed transcripts and proteins between the two stages were identified by comparing the RNA-seq and iTRAQ datasets.…”

“…However, the key enzymes or genes involved in the betalain biosynthesis pathways in pitaya remain elusive. Recently, we obtained nine putative betalain biosynthesis-related genes by analyzing the transcriptomic data of H. polyrhizus [68]. Here we used isobaric tags for relative and absolute quantitation (iTRAQ) to identify key proteins/enzymes that are differentially expressed in pitaya fruit at white vs. red pulp stages in H. polyrhizus , with a focus on those proteins potentially involved in the betalain biosynthesis in pulp coloration of this fruit.…”

The Crossing Effect of Dragon Fruit Plant Caltivars [Hylocereus Sp.] on Yield

“…The red dragon fruit is more and morepopular in thecommunity of this region for at least two considerations, they havethe character-istics as nutrition and contain strong antioxidant and antiinflammatory beneficial in avoiding cancer. This characteristics exist in the fruit due to the betalain pigment content in the fruit having apositive contribution to medicine efficacy [8]. Betalain having deep purple in colour is attractive to cosmetic and food industrial.The whole world is turning towards the use of traditional products and adopting more natural way of life through increased use of herbal products in their daily life [9].…”