A Genome-Wide Identification Study Reveals That HmoCYP76AD1 , HmoDODA α1 and HmocDOPA5GT Involved in Betalain Biosynthesis in Hylocereus .

Betalains are water-soluble nitrogen-containing pigments with multiple bioactivities. Pitayas are the only at large-scale commercially grown fruit containing abundant betalains for consumers. Currently, the key genes involved in betalain biosynthesis remain to be fully elucidated. Moreover, genome-wide analyses of these genes in betalain biosynthesis are not available in betalain-producing plant species. In this study, totally 53 genes related to betalain biosynthesis were identified from the genome data of Hylocereus undatus . Four candidate genes i.e., one cytochrome P-450 R gene ( HmoCYP76AD1 ), two L-DOPA 4,5-dioxygenase genes ( HmoDODAα1 and HmoDODAα2 ), and one cyclo-DOPA 5-O glucosyltransferase gene ( HmocDOPA5GT ) were initially screened according to bioinformatics and qRT-PCR analyses. Silencing HmoCYP76AD1 , HmoDODA α1 , HmoDODA α2 or HmocDOPA5GT resulted in loss of red pigment. HmoDODA α1 displayed a high level of L-DOPA 4,5-dioxygenase activity to produce betalamic acid and formed yellow betaxanthin. Co-expression of HmoCYP76AD1 , HmoDODAα1 and HmocDOPA5GT in Nicotiana benthamiana and yeast resulted in high abundance of betalain pigments with a red color. These results suggested that HmoCYP76AD1 , HmoDODAα1 , and HmocDOPA5GT play key roles in betalain biosynthesis in Hylocereus . The results of the present study provide novel genes for molecular breeding programs of pitaya.