Theoretical and Applied Genetics (2018) 131:861–871
Pyramiding of transgenic Pm3 alleles in wheat results in improved
powdery mildew resistance in the eld
· Susanne Brunner
· Gerhard Herren
· Severine Hurni
· Beat Keller
Received: 22 October 2017 / Accepted: 17 December 2017 / Published online: 4 January 2018
© The Author(s) 2018. This article is an open access publication
Key message The combined eﬀects of enhanced total transgene expression level and allele-speciﬁcity combination
in transgenic allele-pyramided Pm3 wheat lines result in improved powdery mildew ﬁeld resistance without negative
Abstract Allelic Pm3 resistance genes of wheat confer race-speciﬁc resistance to powdery mildew (Blumeria graminis f. sp.
tritici, Bgt) and encode nucleotide-binding domain, leucine-rich repeat (NLR) receptors. Transgenic wheat lines overexpress-
ing alleles Pm3a, b, c, d, f, and g have previously been generated by transformation of cultivar Bobwhite and tested in ﬁeld
trials, revealing varying degrees of powdery mildew resistance conferred by the transgenes. Here, we tested four transgenic
lines each carrying two pyramided Pm3 alleles, which were generated by crossbreeding of lines transformed with single
Pm3 alleles. All four allele-pyramided lines showed strongly improved powdery mildew resistance in the ﬁeld compared to
their parental lines. The improved resistance results from the two eﬀects of enhanced total transgene expression levels and
allele-speciﬁcity combinations. In contrast to leaf segment tests on greenhouse-grown seedlings, no allelic suppression was
observed in the ﬁeld. Plant development and yield scores of the pyramided lines were similar to the mean scores of the corre-
sponding parental lines, and thus, the allele pyramiding did not cause any negative eﬀects. On the contrary, in pyramided line,
Pm3b × Pm3f normal plant development was restored compared to the delayed development and reduced seed set of parental
line Pm3f. Allele-speciﬁc RT qPCR revealed additive transgene expression levels of the two Pm3 alleles in the pyramided
lines. A positive correlation between total transgene expression level and powdery mildew ﬁeld resistance was observed.
In summary, allele pyramiding of Pm3 transgenes proved to be successful in enhancing powdery mildew ﬁeld resistance.
In agricultural practice, two important strategies to control
crop diseases are the use of pesticides and the use of disease-
resistant cultivars. To generate resistant cultivars, a common
approach is the introgression of resistance genes found in the
gene pool of the crop species of interest by multiple steps of
backcrossing (Visscher et al. 1996; Hillel et al. 1990; Tank-
sley and Nelson 1996). A faster and more precise method of
introgression is the genetic transformation of high yielding
crop cultivars with resistance genes of interest (Narusaka
et al. 2013; Rodriguez-Moreno et al. 2017; Lacombe et al.
2010; Mondal et al. 2016). Resistance gene Pm3 from wheat
confers resistance to powdery mildew (Blumeria graminis f.
sp. tritici, Bgt). So far, 17 functional Pm3 alleles have been
identiﬁed (Yahiaoui et al. 2004, 2006; Srichumpa et al. 2005;
Bhullar et al. 2009, 2010). The Pm3 alleles encode nucle-
otide-binding domain; leucine-rich repeat (NLR) type of
receptors which are able to recognize eﬀectors from Bgt and
Communicated by Xiaoquan Qi.
* Beat Keller
Department of Plant and Microbial Biology, University
of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland
Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland