Competitive Performance of Transgenic Wheat Resistant to Powdery Mildew

Olena Kalinina,Simon L Zeller,Bernhard Schmid

doi:10.1371/journal.pone.0028091

Abstract

Genetically modified (GM) plants offer an ideal model system to study the influence of single genes that confer constitutive resistance to pathogens on the ecological behaviour of plants. We used phytometers to study competitive interactions between GM lines of spring wheat Triticum aestivum carrying such genes and control lines. We hypothesized that competitive performance of GM lines would be reduced due to enhanced transgene expression under pathogen levels typically encountered in the field. The transgenes pm3b from wheat (resistance against powdery mildew Blumeria graminis) or chitinase and glucanase genes from barley (resistance against fungi in general) were introduced with the ubiquitin promoter from maize (pm3b and chitinase genes) or the actin promoter from rice (glucanase gene). Phytometers of 15 transgenic and non-transgenic wheat lines were transplanted as seedlings into plots sown with the same 15 lines as competitive environments and subject to two soil nutrient levels. Pm3b lines had reduced mildew incidence compared with control lines. Chitinase and chitinase/glucanase lines showed the same high resistance to mildew as their control in low-nutrient treatment and slightly lower mildew rates than the control in high-nutrient environment. Pm3b lines were weaker competitors than control lines. This resulted in reduced yield and seed number. The Pm3b line with the highest transgene expression had 53.2% lower yield than the control whereas the Pm3b line which segregated in resistance and had higher mildew rates showed only minor costs under competition. The line expressing both chitinase and glucanase genes also showed reduced yield and seed number under competition compared with its control. Our results suggest that single transgenes conferring constitutive resistance to pathogens can have ecological costs and can weaken plant competitiveness even in the presence of the pathogen. The magnitude of these costs appears related to the degree of expression of the transgenes.

Highlights

Advances in biotechnology have allowed the introduction of single genes against fungal pathogens into plants [1], [2]
Phytometers carrying the pm3b gene showed the desired decrease in mildew incidence (Pm3b lines vs. Sb lines phytometer contrast: P,0.001); this decrease was up to five-fold compared with control lines (Figure 1)
Resistance to mildew was substantially increased in Genetically modified (GM) lines carrying the pm3b transgene, as expected, but generally not in GM lines carrying the chitinase and glucanase transgenes, presumably because the latter were introduced into the Swiss wheat variety Frisal which already had an elevated level of resistance to the pathogen

Summary

Introduction

Advances in biotechnology have allowed the introduction of single genes against fungal pathogens into plants [1], [2]. Resistance to a pathogen might reduce plant fitness when the pathogen is absent from the environment Such constitutive resistance is often associated with costs resulting from the allocation of resources to unnecessary defense in a pathogen-free environment, making these resources unavailable for other fitnessrelevant processes [4,5,6]. Another type of cost of resistance, addressed less often, are ecological costs which arise when resistance affects the interactions between a plant and its biotic or abiotic environment in a way that reduces plant fitness [6,7,8]. Those studies mostly considered induced and not constitutive resistance and might have been biased by side-effects of chemical treatments used for defense induction [9,10,11]

Methods

Results

Discussion

Conclusion