Banana21: From Gene Discovery to Deregulated Golden Bananas.

Jean-Yves Paul,Wilberforce Tushemereirwe,James Dale,Robert Harding

doi:10.3389/fpls.2018.00558

Abstract

Uganda is a tropical country with a population in excess of 30 million, >80% of whom live in rural areas. Bananas (Musa spp.) are the staple food of Uganda with the East African Highland banana, a cooking banana, the primary starch source. Unfortunately, these bananas are low in pro-vitamin A (PVA) and iron and, as a result, banana-based diets are low in these micronutrients which results in very high levels of inadequate nutrition. This inadequate nutrition manifests as high levels of vitamin A deficiency, iron deficiency anemia, and stunting in children. A project known as Banana21 commenced in 2005 to alleviate micronutrient deficiencies in Uganda and surrounding countries through the generation of farmer- and consumer-acceptable edible bananas with significantly increased fruit levels of PVA and iron. A genetic modification approach was adopted since bananas are recalcitrant to conventional breeding. In this review, we focus on the PVA-biofortification component of the Banana21 project and describe the proof-of-concept studies conducted in Australia, the transfer of the technology to our Ugandan collaborators, and the successful implementation of the strategy into the field in Uganda. The many challenges encountered and the potential future obstacles to the practical exploitation of PVA-enhanced bananas in Uganda are discussed.

Highlights

Vitamin A (VA) or retinol is an important nutrient which supports vital physiological and developmental functions
In Uganda, 20% of children aged 6 months to 5 years and 19% of women aged 15–49 years suffered from Vitamin A deficiency (VAD) in 2006, predominantly in the low-income demographics within central Ugandan communities, which heavily rely on banana as a staple food (UDHS, 2006)
From the outset in 2005, Banana21 has been on a trajectory to develop lines of East Africa highland bananas (EAHBs) with levels of fruit pro-vitamin A carotenoids (PVACs) that would provide 50% of the estimated average requirement (EAR) of VA with consumption of only 300 g per person per day

Summary

INTRODUCTION

Vitamin A (VA) or retinol is an important nutrient which supports vital physiological and developmental functions. In rural populations of Uganda where EAHBs form a major and sometime unique part of the diet, 20 μg/g dry weight (dw) β-carotene equivalent (β-CE) is the minimum amount of PVA required in banana fruit to provide 50% of the estimated average requirement (EAR) of VA (Paul et al, 2017) Despite their considerable biodiversity, most EAHB varieties grown in East Africa have low levels of essential micronutrients such as iron (Fe), zinc (Zn), and PVACs (Davey et al, 2009; Fungo et al, 2010). This led to the development of Golden Rice 2 (GR2) whereby the use of a maize-derived psy transgene and bacterial crtI, both under the control of the gt promoter, resulted in high levels of PVAC accumulation (Paine et al, 2005) Based on this success, the GR2 strategy was deemed to be the most logical approach to develop VA-biofortified bananas.

Gene abbreviation

Constitutive Constitutive Constitutive

Findings

FINAL REMARKS AND CONCLUSION