Pathogen-inducible Ta-Lr34res expression in heterologous barley confers disease resistance without negative pleiotropic effects.

Rainer Boni,Simon G Krattinger,Beat Keller,Susanne Brunner,Anne Roulin,Harsh Chauhan,Jochen Kumlehn,Goetz Hensel,Justine Sucher

doi:10.1111/pbi.12765

Abstract

SummaryPlant diseases are a serious threat to crop production. The informed use of naturally occurring disease resistance in plant breeding can greatly contribute to sustainably reduce yield losses caused by plant pathogens. The Ta‐Lr34res gene encodes an ABC transporter protein and confers partial, durable, and broad spectrum resistance against several fungal pathogens in wheat. Transgenic barley lines expressing Ta‐Lr34res showed enhanced resistance against powdery mildew and leaf rust of barley. While Ta‐Lr34res is only active at adult stage in wheat, Ta‐Lr34res was found to be highly expressed already at the seedling stage in transgenic barley resulting in severe negative effects on growth. Here, we expressed Ta‐Lr34res under the control of the pathogen‐inducible Hv‐Ger4c promoter in barley. Sixteen independent barley transformants showed strong resistance against leaf rust and powdery mildew. Infection assays and growth parameter measurements were performed under standard glasshouse and near‐field conditions using a convertible glasshouse. Two Hv‐Ger4c::Ta‐Lr34res transgenic events were analysed in detail. Plants of one transformation event had similar grain production compared to wild‐type under glasshouse and near‐field conditions. Our results showed that negative effects caused by constitutive high expression of Ta‐Lr34res driven by the endogenous wheat promoter in barley can be eliminated by inducible expression without compromising disease resistance. These data demonstrate that Ta‐Lr34res is agronomically useful in barley. We conclude that the generation of a large number of transformants in different barley cultivars followed by early field testing will allow identifying barley lines suitable for breeding.

Highlights

To ensure global food security is one of the top challenges in this century
While Ta-Lr34res is only active at adult stage in wheat, Ta-Lr34res was found to be highly expressed already at the seedling stage in transgenic barley resulting in severe negative effects on growth
Our results showed that negative effects caused by constitutive high expression of Ta-Lr34res driven by the endogenous wheat promoter in barley can be eliminated by inducible expression without compromising disease resistance

Summary

Introduction

To ensure global food security is one of the top challenges in this century. The ever-growing world population is the main driver for increasing demand for agricultural products until 2050 (Gerland et al, 2014). Loss of agricultural land and climate change are additional factors that require a higher productivity (Godfray et al, 2010). Plant pathogens are responsible for worldwide crop losses of 10%–16% on average (Chakraborty and Newton, 2011; Oerke, 2006). A major strategy to improve the efficiency of crop production is to enhance plant resistance against diseases by taking advantage of the large diversity of naturally existing resistance genes. To do so, identified resistance genes can be transferred to other crop cultivars by classical breeding or introduced into other plant species by stable genetic transformation. Maize Rxo is an example of a resistance gene that was functionally transferred to the heterologous grass species rice where it mediates resistance against Xanthomonas oryzae pv. Maize Rxo is an example of a resistance gene that was functionally transferred to the heterologous grass species rice where it mediates resistance against Xanthomonas oryzae pv. oryzicola (Zhao et al, 2005)

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Discussion

Conclusion