Native cell-death genes as candidates for developing wilt resistance in transgenic banana plants.

S B Ghag,U K S Shekhawat,T R Ganapathi

doi:10.1093/aobpla/plu037

Abstract

In order to feed an ever-increasing world population, there is an urgent need to improve the production of staple food and fruit crops. The productivity of important food and fruit crops is constrained by numerous biotic and abiotic factors. The cultivation of banana, which is an important fruit crop, is severely threatened by Fusarium wilt disease caused by infestation by an ascomycetes fungus Fusarium oxysporum f. sp. cubense (Foc). Since there are no established edible cultivars of banana resistant to all the pathogenic races of Foc, genetic engineering is the only option for the generation of resistant cultivars. Since Foc is a hemibiotrophic fungus, investigations into the roles played by different cell-death-related genes in the progression of Foc infection on host banana plants are important. Towards this goal, three such genes namely MusaDAD1, MusaBAG1 and MusaBI1 were identified in banana. The study of their expression pattern in banana cells in response to Foc inoculation (using Foc cultures or fungal toxins like fusaric acid and beauvericin) indicated that they were indeed differentially regulated by fungal inoculation. Among the three genes studied, MusaBAG1 showed the highest up-regulation upon Foc inoculation. Further, in order to characterize these genes in the context of Foc infection in banana, we generated transgenic banana plants constitutively overexpressing the three genes that were later subjected to Foc bioassays in a contained greenhouse. Among the three groups of transgenics tested, transformed banana plants overexpressing MusaBAG1 demonstrated the best resistance towards Foc infection. Further, these plants also showed the highest relative overexpression of the transgene (MusaBAG1) among the three groups of transformed plants generated. Our study showed for the first time that native genes like MusaBAG1 can be used to develop transgenic banana plants with efficient resistance towards pathogens like Foc.

Highlights

By the year 2050, the world’s population is expected to be double the present number, making food security for all the most important social issue over the 35 years
Based on the nomenclature of their closest homologues the three genes identified as part of this study were named MusaDAD1, MusaBAG1 and MusaBI1
Genetic engineering of elite banana cultivars for resistance to Fusarium wilt is the only pragmatic goal as there are no established Foc Race 4 cultivars readily available

Summary

Introduction

By the year 2050, the world’s population is expected to be double the present number, making food security for all the most important social issue over the 35 years. Spread of highly virulent Cavendish infecting Foc Race 4 (Buddenhagen 2009) beyond SouthEast Asia and Australia (Butler 2013) is all the more worrisome as there are no established Foc Race 4 resistant cultivars [ several research groups have claimed recovery of somaclonal variants showing promising resistance towards Foc Race 4 (Hwang and Ko 2004)] Owing to their complex ploidy and parthenocarpic fruit development, conventional breeding is laborious and time consuming in edible cultivars of banana and introduction of resistance traits into elite Cavendish varieties through breeding seems to be a distant, if not impossible, goal (Tang 2005; Heslop-Harrison and Schwarzacher 2007).

Methods

Results

Conclusion