title: Evidence for a rhizobia-induced drought stress response strategy in Medicago truncatula.
abstract: Drought stress hampers plant energy and biomass production; however it is still unknown how internal C:N balance and rhizobial symbiosis impact on plant response to water limitation. Here, the effect of differential optimal nitrogen nutrition and root nodule symbiosis on drought stress and rehydration responses of Medicago truncatula was assessed. Two groups of plants were nodulated with Sinorhizobium medicae or Sinorhizobium meliloti--differing in the performance of N fixation; the third group grew in a rhizobia-free medium and received mineral nitrogen fertilizer. In addition to growth analyses, physiological and molecular responses of the two systems were studied using ionomic, metabolomic and proteomic techniques. We found a significant delay in drought-induced leaf senescence in nodulated relative to non-nodulated plants, independent of rhizobial strain and uncoupled from initial leaf N content. The major mechanisms involved are increased concentrations of potassium and shifts in the carbon partitioning between starch and sugars under well-watered conditions, as well as the enhanced allocation of reserves to osmolytes during drought. Consequently, nodulated plants recovered more effectively from drought, relative to non-nodulated M. truncatula. Proteomic data suggest that phytohormone interactions and enhanced translational regulation play a role in increased leaf maintenance in nodulated plants during drought.
authors.affiliation: Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Electronic address: christiana.staudinger@univie.ac.at.
authors.forename: Christiana
authors.initials: C
authors.lastname: Staudinger
authors.affiliation: Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Electronic address: vlora.mehmeti@univie.ac.at.
authors.forename: Vlora
authors.initials: V
authors.lastname: Mehmeti-Tershani
authors.affiliation: Department Environmental Science, Public Univeristy of Navarra Campus Arrosadía, 31006 Pamplona, Spain. Electronic address: erena.gil@unavarra.es.
authors.forename: Erena
authors.initials: E
authors.lastname: Gil-Quintana
authors.affiliation: Department Environmental Science, Public Univeristy of Navarra Campus Arrosadía, 31006 Pamplona, Spain. Electronic address: esther.gonzalez@unavarra.es.
authors.forename: Esther M
authors.initials: EM
authors.lastname: Gonzalez
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Electronic address: florian.hofhansl@univie.ac.at.
authors.forename: Florian
authors.initials: F
authors.lastname: Hofhansl
authors.affiliation: Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Electronic address: gert.bachmann@univie.ac.at.
authors.forename: Gert
authors.initials: G
authors.lastname: Bachmann
authors.affiliation: Department of Ecogenomics and Systems Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Electronic address: stefanie.wienkoop@univie.ac.at.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Wienkoop
mesh_terms: D046913:Medicago truncatula / Q000378:metabolism* / Q000382:microbiology*; D010940:Plant Proteins / Q000378:metabolism*; D012231:Rhizobium; D013312:Stress, Physiological
chemical_list: D010940:Plant Proteins
keywords: Drought stress; Induced tolerance; Leaf senescence; Priming; Stay-green; Symbiosis