Induction and Priming of Plant Defense by Root-Associated Insect-Pathogenic Fungi
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Induction and Priming of Plant Defense by Root-Associated Insect-Pathogenic Fungi Joana Carvalho Cachapa 1 & Nicolai Vitt Meyling 1,2
&
Meike Burow 3
&
Thure Pavlo Hauser 1
Received: 15 September 2020 / Revised: 23 October 2020 / Accepted: 5 November 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Plants evolved in close contact with a myriad of microorganisms, some of which formed associations with their roots, benefitting from carbohydrates and other plant resources. In exchange, they evolved to influence important plant functions, e.g. defense against insect herbivores and other antagonists. Here, we test whether a fungus, Metarhizium brunneum, which is mostly known as an insect pathogen, can also associate with plant roots and contribute to above-ground plant defense. Cauliflower (Brassica oleracea var. botrytis) seeds were sown together with M. brunneum-inoculated rice grains, and the resulting plants subjected to leaf herbivory by the specialist Plutella xylostella. Activity of myrosinases, the enzymes activating glucosinolates, was measured before and after herbivory; larval consumption and plant weight at the end of experiments. Metarhizium brunneum clearly established in the plant roots, and after herbivory myrosinase activity was substantially higher in M. brunneum-treated plants than in controls; before herbivory, M. brunneum-treated and control plants did not differ. Leaf consumption was slightly lower in the M. brunneum-treated plants whereas total biomass and allocation to above- or below-ground parts was not affected by the Metarhizium treatment. Thus, M. brunneum associates with roots and primes the plant for a stronger or faster increase in myrosinase activity upon herbivory. Consistent with this, myrosinase function has been suggested to be rate-limiting for induction of the glucosinolate-myrosinase defense system. Our results show that M. brunneum, in addition to being an insect pathogen, can associate with plant roots and prime plant defense. Keywords Metarhizium brunneum . Brassica oleracea . Root-association . Myrosinase . Defense priming
Introduction Plants live in close association with a multitude of different microorganisms and have done so since they moved onto land ( Blackwell 2000; Retallack 1997). In recent years it has become increasingly clear that some of these microorganisms contribute to the plant’s own defense against antagonizing organisms, among them insect herbivores (Biere and Bennett 2013; Fernández et al. 2014; Pineda et al. 2013;
* Thure Pavlo Hauser [email protected] 1
Section for Organismal Biology, Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark
2
Biotechnology and Plant Health Division, Norwegian Institute of Bioeconomy Research (NIBIO), P.O. Box 115, NO-1431 Ås, Norway
3
DynaMo Center, Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark
Pozo and Azcón-Aguilar 2007; Sanchez-Bel et al. 2016; Wang et al. 2015). Root-associated micro
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