Expression of apoplast-targeted plant defensin MtDef4.2 confers resistance to leaf rust pathogen Puccinia triticina but does not affect mycorrhizal symbiosis in transgenic wheat

Jagdeep Kaur,Alok Adholeya,Dilip Shah,Thomas Clemente,John Fellers,Natalya Nersesian,Kaoutar El-Mounadi,Siva L S Velivelli

doi:10.1007/s11248-016-9978-9

Abstract

Rust fungi of the order Pucciniales are destructive pathogens of wheat worldwide. Leaf rust caused by the obligate, biotrophic basidiomycete fungus Puccinia triticina (Pt) is an economically important disease capable of causing up to 50 % yield losses. Historically, resistant wheat cultivars have been used to control leaf rust, but genetic resistance is ephemeral and breaks down with the emergence of new virulent Pt races. There is a need to develop alternative measures for control of leaf rust in wheat. Development of transgenic wheat expressing an antifungal defensin offers a promising approach to complement the endogenous resistance genes within the wheat germplasm for durable resistance to Pt. To that end, two different wheat genotypes, Bobwhite and Xin Chun 9 were transformed with a chimeric gene encoding an apoplast-targeted antifungal plant defensin MtDEF4.2 from Medicago truncatula. Transgenic lines from four independent events were further characterized. Homozygous transgenic wheat lines expressing MtDEF4.2 displayed resistance to Pt race MCPSS relative to the non-transgenic controls in growth chamber bioassays. Histopathological analysis suggested the presence of both pre- and posthaustorial resistance to leaf rust in these transgenic lines. MtDEF4.2 did not, however, affect the root colonization of a beneficial arbuscular mycorrhizal fungus Rhizophagus irregularis. This study demonstrates that the expression of apoplast-targeted plant defensin MtDEF4.2 can provide substantial resistance to an economically important leaf rust disease in transgenic wheat without negatively impacting its symbiotic relationship with the beneficial mycorrhizal fungus.

Highlights

Wheat is a major food crop grown on about 225 million hectares globally and provides 20 % of the worldwide caloric consumption
This study demonstrates that the expression of apoplast-targeted plant defensin MtDEF4.2 can provide substantial resistance to an economically important leaf rust disease in transgenic wheat without negatively impacting its symbiotic relationship with the beneficial mycorrhizal fungus
In our previously published study, we observed that MtDEF4.2 targeted to the apoplast of transgenic Arabidopsis conferred resistance to the biotrophic obligate oomycete Hyaloperonospora arabidopsidis (Hpa) (Kaur et al 2012)

Summary

Introduction

Wheat is a major food crop grown on about 225 million hectares globally and provides 20 % of the worldwide caloric consumption (http://faostat3.fao. org/). Rust pathogens of the order Pucciniales pose a major threat to food security around the world (Hulbert and Pumphrey 2014). Puccinia triticina (Pt) Eriks, causal agent of wheat leaf rust, is a major threat to wheat production in North America (Kolmer and Hughes 2013). New rust races evolve rapidly limiting the effectiveness of major genes and forcing breeders to find new sources of resistance (Singh et al 2011). While minor gene resistance is more durable, resistance is more quantitative and difficult to identify and transfer into an adapted cultivar (Kolmer 2013). New sources of resistance are often found in the wild relatives of wheat, but transferring resistance to adapted cultivars can be difficult and time consuming. A more durable type of resistance is needed that can withstand new races of Pt

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Conclusion