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.

Increased protein content of chickpea (Cicer arietinum L.) inoculated with arbuscular mycorrhizal fungi and nitrogen‐fixing bacteria under water deficit conditions

“…N‐fixing bacteria and AM fungi have the potential to improve plant growth and alleviate drought stress under water‐limiting conditions . Considering such potential, we aimed at assessing whether inoculation with M. mediterraneum and R. irregularis could improve plant growth, grain yield and protein content under water deficit.…”

A Proteomic View on the Role of Legume Symbiotic Interactions

“…Additionally, authors found an influence of the Rhizobium symbiosis on the abundance levels of stress responsive proteins prior application of the stress treatment. In subsequent works, plants grown under symbiotic conditions were found to present reduced levels of leaf senescence under drought stress, regardless the efficiency of the Rhizobium strain used (Staudinger et al, 2016). Authors concluded that, besides increased jasmonate biosynthesis and potassium ion concentrations, allocation of reserves to osmolytes and a shift in carbon partitioning from starch to sugar are key responses for the observed symbiont-induced stay-green effect.…”

“…Several recent studies have provided broad insights into the systemic effects the legume- Rhizobium symbiotic interaction at the root and, especially, leaf metabolic level (Staudinger et al, 2012, 2016; Desalegn et al, 2016; Turetschek et al, 2016). In all these studies, one of the major response found was related to a significantly induction of the plant translational apparatus and an accumulation of plant proteins involved in stress responses.…”

“…In this line, the effect of Rhizobium in priming plant metabolism in response to salt and drought stress has been analyzed in M. truncatula using a combination of proteomic and metabolomic techniques (Staudinger et al, 2012, 2016). These works highlighted the involvement of another group of nodule proteins in the plant response to drought; the family of lipoxygenases, enzymes related to lipid metabolism and jasmonate biosynthesis.…”

Proposed Research for Innovative Solutions for Chickpeas and Beans in a Climate Change Scenario: The Mediterranean Basin

“…The major mechanisms consist of increased potassium concentrations, balancing the carbon partitioning between starch and sugars and enhance the reserves of osmolytes during drought. Consequently, in general, nodulated plants recovered more effectively from drought than non-nodulated plants [34]. The experimental work, including the number of microbial species and genotypes to be tested, should be divided into several research units.…”