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Mechanism of Abiotic Stress by Arbuscular Mycorrhizae

there are several factors such as metal, temperature, drought etc., how this could be made by the VAM is as given.

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Mechanism of Abiotic Stress by Arbuscular Mycorrhizae

  1. 1. Presented by Nishanth S 2016601106
  2. 2. Introduction
  3. 3. Introduction • Abiotic stresses, such as drought, salinity, extreme temperatures and exposure to pollutants - the primary cause of crop yield loss worldwide (Wang et al., 2003) • Fortunately, some telluric beneficial microorganisms, particularly bacteria and fungi, have the ability to overcome the detrimental effects and to ameliorate plant performance under stress environments (Levy et al., 1983) • Among them, arbuscular mycorrhizal fungi (AMF), belonging to the Glomeromycota phylum, form symbioses with the roots of over 80% of terrestrial plant species (Smith and Read, 2008)
  4. 4. Impact of abiotic stress on Mycorrhizal fungi These fungi are known to improve plant growth and health - by enhancing mineral nutrition and - by increasing tolerance to abiotic and biotic stresses (Turnau and Haselwandter, 2002) The main stages of the mycorrhizal fungus development cycle 1. Germination 2. Colonization 3. Extraradical hyphal elongation 4. Sporulation - could be hampered by the presence of different abiotic stresses.
  5. 5. Impact of abiotic stress on Mycorrhizal fungi 1. An inhibition of spore germination and germinative hyphae elongation. 2. Reduction of the total root colonization. 3. In the case of waterlogging stress, the decrease of mycorrhizal colonization resulted from oxygen deprivation of the host plant root parenchyma. 4. A reduction of vesicle abundance in mycorrhizal roots. 5. The number of BAS (nutrient uptake structures - Rhizophagus irregularis) is reduced in the presence of PAH, fungicide and NaCl (Aranda et al., 2013)
  6. 6. Impact of edaphic & climatic stresses on AMF developmental steps
  7. 7. Mechanism of Abiotic stress tolerance 1. Induction of anti-oxidant system 2. Membrane lipid modification 3. Sequestration 4. Transporters 5. Pollutant transformation 6. Chaperone protein production 7. Trehalose production 1. Anastomosis 2. Hyphal elongation 3. Number of spores 4. Number of entry points & vesicles
  8. 8. Morphological adaptations Anastomosis of disturbed hyphae to form back a connected network after disruption conditions has been suggested as a key mechanism leading to mycorrhizal fungi persistence in harsh environments (de la Providencia et al., 2005; Avio et al., 2006) ANASTOMOSIS The ability to accomplish inter-individual fusion of vegetative cells
  9. 9. Morphological adaptations Increased hyphal elongation Avoid local metal-polluted microenvironments and to reach less contaminated pockets of soil (Cardenas-Flores et al 2011) Increased number of spores A transient increase in the number of spores and BAS structures – because spores are a form of resistance propagules that can survive under adverse conditions.
  10. 10. Morphological adaptations • Increased temperature can enhance carbon allocation, increase acquisition of phosphorus and increase mycorrhizal root colonization rates (Kytöviita and Ruotsalainen, 2007) • During soil waterlogging, an increase of the number of entry points and vesicles (Wu et al., 2013a) Under stressed conditions a mycorrhizal fungus will invest more resources in storage capacity in roots (Staddon et al., 2003)
  11. 11. Biochemical and molecular responses 1. Induction of antioxidant systems MYCORRHIZAL FUNGUS Environmental stress Induce unbalance between production and detoxification of ROS Excess ROS production 1. Proteins 2. Nucleic acids 3. Lipids 4. Lethal cellular alterations
  12. 12. Biochemical and molecular responses Only a few genes encoding proteins putatively involved in ROS homeostasis have been studied in mycorrhizal fungus. Two types of SOD have been identified in mycorrhizal fungus : 1. a Cu, Zn-dependent SOD - GmarCuZn-SOD1 - Gigaspora margarita Lanfranco et al., 2005 - GintSOD1 - R. irregularis González-Guerrero et al., 2007 2. Mn-dependent SOD - GintSOD2 - R. irregularis Ferrol et al., 2009
  13. 13. Biochemical and molecular responses  A second group of antioxidant systems, such as 1. Glutaredoxins 2. Thioredoxins - act as redox regulators of protein thiols and participate to maintain the cell redox balance.  First glomeromycotan dithiol glutaredoxin gene - GintGRX1 (a multifunctional protein with oxidoreductase, peroxidase and glutathione S-transferase activities)  Possess small molecules like glutathione and vitamins B6, C and E that act as antioxidants Glutathione - ROS scavenging Vitamin B6 - modulator of ROS Metallothioneins - ROS scavenging Oxidoreductases
  14. 14. Biochemical and molecular responses  Membrane lipid synthesis is a key event for the establishment of symbiosis and cell membrane properties depend on lipid composition (Wewer et al., 2014) MtMSBP1, encoding a membrane-bound steroid-binding protein (a down-regulation of this gene led to an aberrant mycorrhizal phenotype with thick and septated appressoria and a decreased number of arbuscules) Mycorrhizal Fungi activate triacylglycerol (TAG) biosynthesis to provide carbon skeletons and energy necessary for membrane regenerations under stress 2. MEMBRANE LIPID MODIFICATION
  15. 15. Biochemical and molecular responses • Few genes encoding for a transporter of trace metals have been identified ----- GintZnT1 - a putative Zn transporter (González-Guerrero et al., 2005) GiArsA - a putative arsenite efflux pump (González-Chávez et al., 2011) GintABC1 - an ATP-binding cassette (ABC) transporter, able to transport Cu and Cd (González-Guerrero et al., 2010) Each aquaporin gene of plants may respond differently to mycorrhizal colonization and stress imposed (drought, cold or salinity). GintAQPF1 and GintAQPF2 – drought condition GintAQP1 - salt stress 3. TRANSPORTERS
  16. 16. Biochemical and molecular responses • Prevent misfolding or aggregation of proteins generally induced by abiotic stresses. • Specific genes encoding for a 14-3-3 protein and the luminal binding protein (BiP) - identified under drought and saline stress. • The 14-3-3 protein family - wideranging regulatory functions by acting as phosphoserine/phosphothreonine- binding proteins. 4. CHAPERON PROTEIN PRODUCTION
  17. 17. Biochemical and molecular responses • Under abiotic stresses : The increase of secretory activity and accumulation of unfolded proteins within the ER --- result in the induction of BiP {transiently bind to unfolded proteins and to prevent permanent misfolding or aggregation with the subsequent loss of their function • The glomalin protein sequence found in R. irregularis (DAOM197198) encodes a putative heat shock protein 60 (Gadkar and Rillig, 2006)
  18. 18. Biochemical and molecular responses A common reserve carbohydrate in fungi but also a molecule involved in defense reaction. Trehalose protects the cells by 1. stabilizing cell structures and 2. enables proteins to maintain their native conformation 5. TREHALOSE PRODUCTION
  19. 19. Biochemical and molecular responses FUNGAL CELL Activation of trehalose metabolism enzymes (transcriptionally and/or post-transcriptionally) Accumulation of Trehalose TREHALOSE PRODUCTION
  20. 20. References 1. Ingrid Lenoir, Joël Fontaine, Anissa Lounès-Hadj Sahraoui, 2016. Arbuscular mycorrhizal fungal responses to abiotic stresses: A review,, Phytochemistry 123: 4–15 2. Aranda, E. et al., 2013. Role of arbuscular mycorrhizal fungus Rhizophagus custos in the dissipation of PAHs under root-organ culture conditions. Environmental Pollution 181: 182–189 3. Wewer, V., Brands, M., Dörmann, P., 2014. Fatty acid synthesis and lipid metabolism in the obligate biotrophic fungus Rhizophagus irregularis during mycorrhization of Lotus japonicus. Plant J. 79: 398–412

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