Overexpression of the IbMYB1 gene in an orange‐fleshed sweet potato cultivar produces a dual‐pigmented transgenic sweet potato with improved antioxidant activity

Abstract

The R2R3-type protein IbMYB1 is a key regulator of anthocyanin biosynthesis in the storage roots of sweet potato [Ipomoea batatas (L.) Lam]. Previously, we demonstrated that IbMYB1 expression stimulated anthocyanin pigmentation in tobacco leaves and Arabidopsis. Here, we generated dual-pigmented transgenic sweet potato plants that accumulated high levels of both anthocyanins and carotenoids in a single sweet potato storage root. An orange-fleshed cultivar with high carotenoid levels was transformed with the IbMYB1 gene under the control of either the storage root-specific sporamin 1 (SPO1) promoter or the oxidative stress-inducible peroxidase anionic 2 (SWPA2) promoter. The SPO1-MYB transgenic lines exhibited higher anthocyanin levels in storage roots than empty vector control (EV) or SWPA2-MYB plants, but carotenoid content was unchanged. SWPA2-MYB transgenic lines exhibited higher levels of both anthocyanin and carotenoids than EV plants. Analysis of hydrolyzed anthocyanin extracts indicated that cyanidin and peonidin predominated in both overexpression lines. Quantitative reverse transcription-polymerase chain reaction analysis demonstrated that IbMYB1 expression in both IbMYB1 transgenic lines strongly induced the upregulation of several genes in the anthocyanin biosynthetic pathway, whereas the expression of carotenoid biosynthetic pathway genes varied between transgenic lines. Increased anthocyanin levels in transgenic plants also promoted the elevation of proanthocyanidin and total phenolic levels in fresh storage roots. Consequently, all IbMYB1 transgenic plants displayed much higher antioxidant activities than EV plants. In field cultivations, storage root yields varied between the transgenic lines. Taken together, our results indicate that overexpression of IbMYB1 is a highly promising strategy for the generation of transgenic plants with enhanced antioxidant capacity.

Genome-wide identification of cassava R2R3 MYB family genes related to abscission zone separation after environmental-stress-induced abscission

“…The R2R3 MYB protein SlAN2 from tomatoes elevates ethylene synthesis12. IbMYB1 from sweet potatoes displays increased antioxidant activities in transgenic plants compared with empty vector control plants13. PtsrMYB from trifoliate oranges is up-regulated by abiotic stresses (dehydration, salt, cold and ABA treatment) and decreases the levels of reactive oxygen species and increases the levels of polyamines14.…”

Sweet potato expressing the rice Zn transporter <i>OsZIP4</i> exhibits high Zn content in the tuber

“…Previous report mentioned that sweet potato has high fiber, low saturated fat and an abundance of antioxidants (Park et al 2014). Moreover, sweet potato is also considered to be tolerant to environmental stress.…”

Functional components in sweetpotato and their genetic improvement

“…By conducting a gene expression analysis using purple-fleshed cultivars and transformation experiments using sweetpotato leaves and calli, Mano et al (2007) demonstrated that one of the MYB-type transcription factors in sweetpotato, IbMYB1, is responsible for anthocyanin accumulation in storage roots. Overexpression of the IbMYB1 gene successfully induced anthocyanin accumulation in the storage roots of an orange-fleshed sweetpotato cultivar, resulting in higher radical scavenging activity (Park et al 2015b). Tanaka et al (2012) compared the structure of the IbMYB1 genes between cultivars with high-anthocyanin content and cultivars without anthocyanins, and they found that distinct IbMYB1 copies, named IbMYB1-2a and IbMYB1-2b , are shared only in the high-anthocyanin cultivars and their common ancestor ‘Yamagawamurasaki’.…”

“…Park et al (2015b) reported that the transgenic plants overexpressing IbMYB1 showed an elevated total polyphenol level. In these plants, the gene expression of phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-hydroxycinnamoyl-CoA ligase (4CL), all of which are involved in the early steps of both anthocyanin and CQA biosynthesis, was upregulated.…”