title: The cost of surviving nitrogen excess: energy and protein demand in the lichen Cladonia portentosa as revealed by proteomic analysis.
abstract: Different nitrogen forms affect different metabolic pathways in lichens. In particular, the most relevant changes in protein expression were observed in the fungal partner, with NO3-mostly affecting the energetic metabolism and NH4+affecting transport and regulation of proteins and the energetic metabolism much more than NO3-did. Excess deposition of reactive nitrogen is a well-known agent of stress for lichens, but which symbiont is most affected and how, remains a mystery. Using proteomics can expand our understanding of stress effects on lichens. We investigated the effects of different doses and forms of reactive nitrogen, with and without supplementary phosphorus and potassium, on the proteome of the lichen Cladonia portentosa growing in a 'real-world' simulation of nitrogen deposition. Protein expression changed with the nitrogen treatments but mostly in the fungal partner, with NO3-mainly affecting the energetic metabolism and NH4+also affecting the protein synthesis machinery. The photobiont mainly responded overexpressing proteins involved in energy production. This suggests that in response to nitrogen stress, the photobiont mainly supports the defensive mechanisms initiated by the mycobiont with an increased energy production. Such surplus energy is then used by the cell to maintain functionality in the presence of NO3-, while a futile cycle of protein production can be hypothesized to be induced by NH4+excess. External supply of potassium and phosphorus influenced differently the responses of particular enzymes, likely reflecting the many processes in which potassium exerts a regulatory function.
authors.affiliation: Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Bloco C2, 1749-016, Lisbon, Portugal. ssmunzi@fc.ul.pt.
authors.forename: Silvana
authors.identifier: http://orcid.org/0000-0002-0071-7699
authors.initials: S
authors.lastname: Munzi
authors.affiliation: Centre for Ecology and Hydrology (CEH) Edinburgh, Bush Estate, Penicuik, EH26 0QB, UK.
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Sheppard
authors.affiliation: Centre for Ecology and Hydrology (CEH) Edinburgh, Bush Estate, Penicuik, EH26 0QB, UK.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Leith
authors.affiliation: Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Bloco C2, 1749-016, Lisbon, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Cruz
authors.affiliation: Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Bloco C2, 1749-016, Lisbon, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Branquinho
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro, 2, 53100, Siena, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Bini
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro, 2, 53100, Siena, Italy.
authors.forename: Assunta
authors.initials: A
authors.lastname: Gagliardi
authors.affiliation: Department of Life Sciences, University of Siena, Via Pier Andrea Mattioli, 4, 53100, Siena, Italy.
authors.forename: Giampiero
authors.initials: G
authors.lastname: Cai
authors.affiliation: Department of Biological, Geological and Environmental Sciences, University of Bologna, Via Irnerio, 42, 40126, Bologna, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Parrotta
mesh_terms: D000641:Ammonia / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D015180:Electrophoresis, Gel, Two-Dimensional; D004734:Energy Metabolism / Q000502:physiology; D008011:Lichens / Q000378:metabolism* / Q000502:physiology; D013058:Mass Spectrometry; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism* / Q000502:physiology; D010788:Photosynthesis; D040901:Proteomics
chemical_list: D009566:Nitrates; D002734:Chlorophyll; D000641:Ammonia; D009584:Nitrogen; D000077194:Chlorophyll A
keywords: Ammonium; Molecular mechanism; Mycobiont; Nitrate; Photobiont; Stress response