Plant-Fungi Interactions

Transcription

1 Plant-Fungi Interactions

2 Mutualistic Plant-Fungi Interactions Stem and Leaves Phyllosphere fungi Root Rhizosphere fungi Root endophytes Mycorrhizal fungi

3 Endophyte: An endosymbiont, usually a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. The isolation procedure and the use of surface sterilization is important to suggest that a microbe is an endophyte

4 Ecological benefits of fungal endophytes

5 Endofiti fungini sono comuni simbionti delle piante Endofiti fungini di Tipo I (Clavicipitaceae, Ascomiceti) Una sola famiglia di funghi (ord. Hypocreales) Trasmessi verticalmente attraverso i semi Principalmente coinvolti nella resistenza a erbivori (insetti o vertebrati) attraverso la produzione di alcaloidi Endofiti fungini di Tipo II (Non-Clavicipitaceae) Molti generi diversi di Ascomiceti e Basidiomiceti Trasmessi verticalmente o orizzontalmente Coinvolti nella resistenza a stress ambientali diversi

6 Clavicipitaceae Endophytes Claviceps Epichloe (Tel. Neotyphodium) Defensive Mutualism Production of secondary metabolites (Alkaloids) Endophyte infected grass can harm vertebrate herbivores

7 Clavicipitales Endophytes Schematic Representation Showing the Combined Effects of Epichloë Endophyte-Produced Defenses (Alkaloids) and the Plant s Own Defenses on Plant Resistance to Insects Belonging to Two Different Feeding Guilds In the case represented in the figure, the endophyte generates a profile of effective alkaloids (EAs) against both chewing and sap-sucking insect species. Plant defenses, mediated by the jasmonic acid (JA) and salicylic acid (SA) pathways, are effective only against chewing insects because, according to the model, defenses against sap-sucking insects are dependent on SA and the SA pathway is repressed by the endophyte. The model predicts that plant resistance to sapsucking insects is solely dependent on the effectiveness of the alkaloids produced by the fungus, whereas resistance to chewing insects is mediated by both EA-based and JA-dependent defenses. Arrows indicate positive regulation and truncated connectors indicate inhibition or negative regulation. Unbroken lines indicate functional connections that are well documented in the literature; broken lines denote assumptions of the model that require further testing by direct experimentation.

8 The interactions among shoot and root herbivores, foliar and root endophytes, and mycorrhizae presented in terms of how well known these interactions are on the basis of current literature. The figure presents these interactions for (a) grass and (b) herbaceous systems; only the interactions between foliar endophytes and herbivores and mycorrhizae and shoot herbivores have been studied for trees.

9 Endophytes associated with medicinal plants are an interesting source of bioactive secondary metabolites Endophytes are the microorganisms that occur within the tissues of the plants without causing any noticeable symptoms and diseases to the host. In general, fungi and bacteria are the most common microbes exist as endophytes in plants. In recent years, endophytic fungi are known to produce several bioactive secondary metabolites, mainly used in pharmaceutical, agricultural and industrial applications.

10 Root Rhizosphere fungi Root endophytes Mycorrhizal fungi Some fungi, because of their filamentous organization, can colonise all different compartments Rhizosphere fungi: Biocontrol Nutrient acquisition Organic matter degradation

11 Some biocontrol fungi can directly attack fungal pathogens in the rhizosphere Mycoparasitism Trichoderma (Tel. Hypocrea)

12 Mycorrhiza

13 Mineral Nutrients Mycorrhiza Myco (= fungus) rhiza (= root) Carbohydrates

14 Distribution and abundance of mycorrhiza The study of plants without their mycorrhizas is the study of artefacts. The majority of plants, strictly speaking, do not have roots; they have mycorrhizas.

15 Mycorrhizal types (morphology-based) Ectomycorrhiza Endomycorrhiza: Ectoendomycorrhiza: Arbuscular Ericoid in Orchids in Gymnosperm seedlings Arbutoid Monotropoid

16 Ectomycorrhiza Arbuscular Mycorrhiza Ericoid and Orchid Mycorrhiza Ectomycorrhiza Endomycorrhiza

17 Summary

18 Ectomicorrize Fitobionti Micobionti (~5% delle Spermatofite) ca specie (~6000 specie fungine)

19 Ectomicorrize Fitobionti Emisfero boreale piante forestali (Pinaceae, Fagaceae, Betulaceae, Salicaceae ) Emisfero australe Nothofagus, Eucalyptus Hanno sia ECM che AM (e actinorrize): Alnus, Populus, Salix Casuarina, Allocasuarina, Eucalyptus, Melaleuca e Acacia

20 Poche specie erbacee formano ectomicorrize Polygonum viviparum Kobresia (Dryas)

21 Ectomicorrize Basidiomiceti Agaricales e Boletales (Amanita, Boletus, Russula, Lactarius, Laccaria, Hebeloma ) Hymenogastrales (Hymenogaster) Sclerodermatales (Pisolithus) Micobionti Ascomiceti Tuber Elaphomyces Cenococcum Zigomiceti Endogonaceae

22 Different anatomy of ECM in angiosperms and gymnosperms

23 Ectomicorrize: differenze tra angiosperme e gimnosperme Morfologia esterna della radice micorrizata

24 Endomicorrize Arbuscolari Fitobionti Briofite, Pteridofite, Spermatofite (~80% piante vascolari) Piante erbacee (non hanno AM: Juncaceae, Cyperaceae, Caryophyllaceae, Cruciferae, Chenopodiaceae) Piante arboree: - Fraxinus (Oleaceae) - piante da frutto (Rosaceae) - alcune Gimnosperme arboree (es. Gingko) - Populus e Salix (Salicaceae) hanno sia AM sia ECM

25 Endomicorrize Arbuscolari Phylum Glomeromycota (~150 specie) (Glomus, Gigaspora, Acaulospora, Scutellospora, Sclerocystis, Entrophospora) Micobionti Schuessler et al. 2001

26 The success of mycorrhiza in time and space: about fungi and plants Terziario Cretaceo Devoniano Ordoviciano AM are very ancient associations Distributed world-wide

27 Mya Glomeromycota had already appeared when the first plants colonised land AM fungi Land plants Angiosperms Legumes Proterozoico Paleozoico Mesozoico Cenozoico Cretaceo Giurassico Triassico Carbonifero

28 The first land plants were lacking roots

29 Other mycorrhizal types are much younger than AM

30 Distribution of mycorrhizal types (D. Read)

31 Mycorrhizal fungi are a bridge between the root and the soil Soil texture is improved

32 Benefits for the Fungus Sugar uptake Life cycle completion Laccaria laccata Thanks to the plant-derived carbon, the extraradical mycelium grows and explores larger soil volumes

33 Benefits for the Plant - Mineral Nutrition (N, P) - Water uptake - Pathogen protection - Protection from abiotic stress - Biodiversity non myc myc Growth effect

34 The extraradical mycorrhizal mycelium is essential for nutrient and water uptake

35 Why mycorrhiza? Fine roots and root hairs mine the soil for nutrients. Mycorrhizal hyphae do this even better. Root hair Smallest hyphae Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th diameter of root hair Increased surface area Surface Area/Volume = 2/r

36 The depletion zone Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone

37 Soil Organic Matter (SOM) Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone C C NH 2 C C + NH 3 Breakdown of organic matter

38 BIODIVERSITA La comunità di funghi micorrizici arbuscolari influisce direttamente sulla composizione della comunità vegetale, aumentandone la biodiversità e la produttività

39 Influenza dei funghi AM sul successo riproduttivo e sulla competizione tra specie vegetali Aumentando il N di specie fungine aumenta il numero e la produttività delle specie vegetali Concetto di compatibilità funzionale

40 The Common Mycorrhizal Network

41 Compartmented microcosms to study the role of CMNs in monocultures and mixed culture Microcosms, consisting of two plant individuals, were set up in compartmented containers subdivided by nylon mesh screens (25 and 65 μm, respectively, as indicated). Both types of screens are pervious for fungal hyphae but not for roots and allow the separation into two RHCs, a HC, and a LHC for supplying 15N and 33P labels. The plants used were flax (F) and sorghum (S) either as a pair of conspecific plants (F:F, S:S) as a model of monoculture or in combination (F:S) as a model of a mixed culture.

42 A Common Mycorrhizal Network (CMN) can facilitate resource sharing Intercropping with sorghum drastically enhanced flax s growth. Nutrient uptake was facilitated via the CMN Impact of a CMN in monocultures and mixed culture. The presence of a CMN of G. intraradices strongly enhanced the biomass production of flax in mixed culture with sorghum. Sorghum was not significantly affected by the presence of a CMN in the mixed culture with flax. The flax plants grew significantly faster in the flax/sorghum mixed cultures than in the flax monocultures. Conversely, the growth of sorghum was only marginally influenced by the culture system.

43 Terms of trade in CMNs between flax and sorghum formed by G. intraradices and G. mosseae In this scheme, the carbon investment of the plants is depicted by green arrows. In both CMNs, sorghum invested more than twice as much than flax in terms of carbon. The return, in the form of the nutrients phosphorus (P) and nitrogen (N), is illustrated by the yellow and orange arrows, respectively. In the CMN formed by G. intraradices, the return was extremely uneven; flax obtained 80% to 94% of the nutrients delivered by the CMN, and sorghum, the main investor, obtained only 6% to 20%. In the CMN formed by G. mosseae, both flax and sorghum received an approximately equal share of the nutrients delivered by the CMN, but because flax invested less than half as much carbon compared with sorghum, it still benefited from its neighbor. Plants may cooperatively maintain CMNs without causing exorbitant costs to any of the partners joined in the network. This may explain how the presence of AMF promotes the productivity and diversity of plant communities (van der Heijden et al., 1998).