Abstract
The red flesh trait gives red pitayas more healthful components and a higher price, while the genetic mechanism behind this trait is unknown. In this manuscript, transcriptome analysis was employed to discover the genetic differences between white and red flesh in pitayas. A total of 27.99 Gb clean data were obtained for four samples. Unigenes, 79,049 in number, were generated with an average length of 1333 bp, and 52,618 Unigenes were annotated. Compared with white flesh, the expression of 10,215 Unigenes was up-regulated, and 4853 Unigenes were down-regulated in red flesh. The metabolic pathways accounted for 64.6% of all differentially expressed Unigenes in KEGG pathways. The group with high betalain content in red flesh and all structural genes, related to betalain biosynthesis, had a higher expression in red flesh than white flesh. The expression of the key gene, tyrosine hydroxylase CYP76AD1, was up-regulated 245.08 times, while 4,5-DOPA dioxygenase DODA was up-regulated 6.46 times. Moreover, the special isomers CYP76AD1α and DODAα were only expressed in red flesh. The competitive anthocyanin biosynthesis pathway had a lower expression in red flesh. Two MYB transcription factors were of the same branch as BvMYB1, regulating betalain biosynthesis in beet, and those transcription factors had expression differences in two kinds of pitayas, which indicated that they should be candidate genes controlling betalain accumulation in red pitayas. This research would benefit from identifying the major gene controlling red flesh trait and breed new cultivars with the red flesh trait. Future research should aim to prove the role of each candidate gene in betalain biosynthesis in red pitayas.
Highlights
IntroductionCommonly known as dragon fruit, belong to the genus Hylocereus of the orderCaryophyllales
Pitayas, commonly known as dragon fruit, belong to the genus Hylocereus of the orderCaryophyllales
Q30 were over 95%, which means the Illumina sequencing was of high quality for further analysis (Table S1)
Summary
Commonly known as dragon fruit, belong to the genus Hylocereus of the orderCaryophyllales. Commonly known as dragon fruit, belong to the genus Hylocereus of the order. Hylocereus species originate from Latin America and are cultivated in tropical and subtropical regions worldwide [1,2]. There are several types of pitayas, such as Hylocereus undatus, Hylocereus costaricensis, and Hylocereus megalanthus. H. undatus and H. costaricensis are the most widely cultivated and have the same red fruit skin color but different flesh colors, white. The red-violet betacyanins and yellow-orange betaxanthins, contribute to the red flesh color [3]. H. costaricensis has a high Betalain content, but some agricultural traits are worse than those of H. undatus. Understanding the genetic mechanism of the red flesh trait will be beneficial for breeding new cultivars carrying both red flesh and better agricultural traits
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