Golden bananas in the field: elevated fruit pro‐vitamin A from the expression of a single banana transgene

Abstract

SummaryVitamin A deficiency remains one of the world's major public health problems despite food fortification and supplements strategies. Biofortification of staple crops with enhanced levels of pro‐vitamin A (PVA) offers a sustainable alternative strategy to both food fortification and supplementation. As a proof of concept, PVA‐biofortified transgenic Cavendish bananas were generated and field trialed in Australia with the aim of achieving a target level of 20 μg/g of dry weight (dw) β‐carotene equivalent (β‐CE) in the fruit. Expression of a Fe'i banana‐derived phytoene synthase 2a (MtPsy2a) gene resulted in the generation of lines with PVA levels exceeding the target level with one line reaching 55 μg/g dw β‐CE . Expression of the maize phytoene synthase 1 (ZmPsy1) gene, used to develop ‘Golden Rice 2’, also resulted in increased fruit PVA levels although many lines displayed undesirable phenotypes. Constitutive expression of either transgene with the maize polyubiquitin promoter increased PVA accumulation from the earliest stage of fruit development. In contrast, PVA accumulation was restricted to the late stages of fruit development when either the banana 1‐aminocyclopropane‐1‐carboxylate oxidase or the expansin 1 promoters were used to drive the same transgenes. Wild‐type plants with the longest fruit development time had also the highest fruit PVA concentrations. The results from this study suggest that early activation of the rate‐limiting enzyme in the carotenoid biosynthetic pathway and extended fruit maturation time are essential factors to achieve optimal PVA concentrations in banana fruit.

Pro‐vitamin A carotenoids in East African highland banana and other Musa cultivars grown in Uganda

“…There remains, however, persistently high levels of VAD particularly in remote hard-to-reach areas that will only be addressed through more innovative strategies. As such, where bananas are a major component of the daily carbohydrate intake, their biofortification with pVACs has the potential to help address VAD and therefore has become a key focus of local and international research and collaboration (Buah, Mlalazi, Khanna, Dale, & Mortimer, 2016;Paul et al, 2017). By increasing the amount of essential nutrients in staple food crops, biofortification aims to target malnourished populations in a more economically viable and sustainable way.…”

“…In contrast, the commercial Cavendish cultivar "Williams" has only 57 μg/100 g fw β-carotene (Englberger, Wills, et al, 2006). There is circumstantial evidence that both time of fruit development, and the prevailing environmental conditions plays a critical role in this pVAC variability (Paul et al, 2017). There is circumstantial evidence that both time of fruit development, and the prevailing environmental conditions plays a critical role in this pVAC variability (Paul et al, 2017).…”

An overview of agriculture, nutrition and fortification, supplementation and biofortification: Golden Rice as an example for enhancing micronutrient intake

“…Increases of not only iron and zinc [88], but also folate [89,90] and pro-vitamin A in staple crops of the poor [42,49,91] are all extremely important for human health. All of them have been achieved using gmo-technology, where conventional breeding was not possible.…”

“…Transgenesis has also be used, with various levels of success so far, to introduce provitamin A traits into other important food security crops where (previously considered as) conventional plant breeding techniques could not be effective: cassava, sorghum and plantain (also called cooking banana) [5,91], all after Golden Rice's technology was published [42,49]. Professor Beyer's molecular pathway engineering expertise was sought by all these projects at one time or another.…”

I Have a Dream: Organic Movements Include Gene Manipulation to Improve Sustainable Farming

“…To be compatible with organic farming, it seems to me essential that any transgene flow is excluded by restricting these manipulations to cisgenesis or genome editing approaches that do not introduce any foreign DNA, unless banana cultivars are used that are proven to be completely infertile. The authors' lab has shown, in a recent proof of concept [21] using the Cavendish cultivar, that a substantial increase in pro-vitamin A can be obtained by the integration of banana gene sequences exclusively. The data show that the use of a banana promoter as well as the banana phytoene synthase 2a gene results in bananas expressing a 10-fold higher level of pro-vitamin A which is reflected in the golden flesh, hence the name golden banana.…”