The molecular basis of the reduction in the number of nodules that legumes form in soils with low pH are not clear yet. It has been propose that the elicitation of a hypersensitive reaction(HR) is part of the mechanism by which the plant controls infection, and therefore, regulates nodulation. The aim of the Project is to test whether the reduction in the number of nodules at low pH is associated to a stronger elicitation response in the plant triggered by the acid stress. In order to achieve this objective different Medicago spp will be used including two acidic resistant. These different Medicago spp will be inoculated with acid-sensitive and tolerant Rhizobium strains. Cytological and morphological features of the infective process under acidic and neutral pH will be analyzed and compared in order to test whether the low pH causes an increase in the number of aborted infection threads. This, together with the measurement of the evolution of endogenous ethylene as well as the analysis of the level of expression of proteins involve in plant defense mechanisms will give us some more evidences to know whether a HR of the plant is involved in the control of nodulation in acidic conditions.
Training content (objective, benefit and expected impact) The objective of the training is the study of the role of the plant in the control of nodulation during the symbiosis between Rhizobium and legumes under acidic conditions. This study will help to achieve a better understanding of the molecular basis of the R. meliloti-Medicago symbiotic interaction under different environmental conditions. This knowledge might in later stages provide a tool for improving the efficiency of this symbiosis under special conditions as low pH.