The Chemical Ecology of Tree-Herbivore-Pathogen Interactions
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Tripartite relationships: The chemical ecology of tree-herbivore-pathogen interactions DISSERTATION To Fulfill the Requirements for the Degree of „doctor rerum naturalium“ (Dr. rer. nat.) Submitted to the Council of the Faculty of Biological Sciences of the Friedrich Schiller University Jena by Franziska Eberl (Master of Science) born on 19.06.1990 in Halle (Saale), Germany Reviewers: Prof. Dr. Ralf Oelmüller Matthias-Schleiden-Institut Friedrich Schiller University Jena Prof. Dr. Jonathan Gershenzon Department of Biochemistry Max Planck Institute for Chemical Ecology Prof. Dr. Richard L. Lindroth Department of Entomology University of Wisconsin-Madison, WI, USA Date of defense: May 23rd, 2019 Table of contents 1. INTRODUCTION .............................................................................................................................4 1.1. Fungal colonization and anti-fungal defenses in plants .....................................................4 1.2. Plant-herbivore interactions.................................................................................................7 1.3. Complex tripartite interactions ......................................................................................... 10 1.4. The study organisms: black poplar, poplar leaf rust and gypsy moth ............................ 11 1.5. Aim of the thesis ................................................................................................................ 15 2. OVERVIEW OF MANUSCRIPTS ................................................................................................... 16 2.1. Manuscript I ........................................................................................................................ 16 2.2. Manuscript II ....................................................................................................................... 17 2.3. Manuscript III ...................................................................................................................... 18 2.4. Manuscript IV ..................................................................................................................... 19 3. MANUSCRIPT I ............................................................................................................................ 20 4. MANUSCRIPT II ........................................................................................................................... 56 5. MANUSCRIPT III .......................................................................................................................... 70 6. MANUSCRIPT IV .......................................................................................................................... 84 7. DISCUSSION .............................................................................................................................. 119 7.1. Rust infection changes physiology and metabolism in black poplar ............................ 119 7.2. Multiple attacks in black poplar reduce anti-herbivore defense .................................. 123 7.3. Consequences of multiple attacks in black poplar for herbivores ................................ 125 7.4. Conclusion and Outlook ................................................................................................... 129 8. SUMMARY................................................................................................................................. 131 9. ZUSAMMENFASSUNG .............................................................................................................. 134 10. BIBLIOGRAPHY .......................................................................................................................... 136 11. ACKNOWLEDGEMENTS ............................................................................................................ 147 12. EIGENSTÄNDIGKEITSERKLÄRUNG ........................................................................................... 149 13. Curriculum Vitae....................................................................................................................... 150 14. Supplementary Data ................................................................................................................. 154 14.1. Manuscript I – Supplementary data ................................................................................ 154 14.2. Manuscript II – Supplementary data ............................................................................... 158 14.3. Manuscript III – Supplementary data .............................................................................. 163 14.4. Manuscript IV – Supplementary data .............................................................................. 175 1. Introduction 1. INTRODUCTION One third of the landmass of our planet is covered with forest (FAO 2015), and the immense ecological importance of the trees growing in these forests is almost impossible to describe. Beside their atmospheric impact by carbon fixation, oxygen production and emission of volatile organic compounds, trees shape the biotic environment in these ecosystems. Each tree harbors a huge diversity of microbial as well as vertebrate and invertebrate species, which inhabit below- and aboveground tissues. Microbes, especially bacteria and fungi, might have beneficial or detrimental effects on their hosts as symbionts or pathogens, respectively. At the same time, plants are continuously exposed to herbivores, especially insects, which feed on their leaves, roots and other tissues. Trees play a pivotal role in forest ecosystems as their longevity and large size offers numerous possibilities for interactions with other organisms, as compared to short-lived and small-sized herbs. This makes woody plants ideal study organisms to elucidate complex ecological interactions. Nevertheless, studies on plant-insect or plant-microbe interactions have been carried out predominantly with herbs and crop plants. The characterization of trees and their biotic environment, however, will open up new perspectives and provide knowledge to elucidate the chemical interactions between multiple organisms in complex ecosystems. 1.1. Fungal colonization and anti-fungal defenses in plants Prevalence and importance of leaf pathogens Microbial species occur in all ecosystems of the world, and are often associated with other organisms which they colonize internally or externally, such as plants and animals. Plant-microbe associations have been described for a wide range of microbial species including bacteria, protists, archaea and fungi (Berg et al. 2016; Hardham 2007). Fungi can colonize every organ of a plant, i.e. leaves, roots, stems, flowers and, in case of trees, also bark and wood (Baldrian 2017). They are hence universally abundant, and under natural conditions every plant is associated with fungi. However, the role of fungi in these associations may take different forms, ranging from mutualistic (e. g. mycorrhizae), commensal (the microbe benefits without negative effects on its plant host) to pathogenic (as causing agent of diseases). Other fungi, the saprophytes, only 4 1. Introduction colonize dead plant tissue and therefore do not influence plant physiology actively but play an important role in nutrient cycling (Azcón-Aguilar & Barea 2015). In this thesis I focus on leaf pathogens, disease-causing fungi that inhabit the foliage of plants. Leaf pathogens can be classified according to their life style into biotrophic or necrotrophic pathogens (Glazebrook 2005). Biotrophic pathogens require living plant cells from which they withdraw nutrients, often by specialized hyphae called haustoria (Vögele & Mendgen 2003). Necrotrophic pathogens, on the other hand, kill host cells to deprive nutrients from dead or dying tissue. Some pathogens, the hemibiotrophs, are able to switch from one life style to the other, usually passing through a biotrophic phase first before turning into necrotrophs (Ferreira et al. 2006). Pathogens that infect crop plants and thereby affect economic yields have been studied most intensively. Well known examples are molds such as the necrotrophic Botrytis cinerea infecting grapes and wine, biotrophic rusts such as Puccinia graminis infecting wheat, and the hemibiotrophic Colletotrichum spp. which infect a wide range of vegetables (Dean et al. 2012). Plants infected by necrotrophic pathogens suffer from the loss of photosynthesizing tissue, while plants infected by biotrophic pathogens are deprived of nutrients. Both infection modes reduce carbon fixation in their host plants, lower levels of stored reserves and result in less investment into growth and reproduction. To protect plants, especially crops, from pathogen-related damage great efforts have been made to breed resistant varieties. However, in order to select for resistant genotypes it is necessary to have a detailed understanding of pathogen-recognition and anti- pathogen defense in plants. Recognition and defense against fungal pathogens in plants Pathogens can enter the plant matrix through natural openings, such as stomata, or by wounds, insect vectors (Kluth et al. 2002) or pegs and appressoria, specialized fungal structures that penetrate the plant epidermis (Dean et al. 2012). Once inside the host, the pathogen is recognized by the plant through pathogen-specific molecules (Dodds & Rathjen 2010). Non-specific recognition occurs by detection of “pathogen-associated molecular patterns” (PAMPs; sometimes referred to as