Abstract
Arbuscular Mycorrhiza and Root Nodule Symbiosis are symbiotic interactions with a high benefit for plant growth and crop production. Thus, it is of great interest to understand the developmental process of these symbioses in detail. We analysed very early symbiotic responses of Medicago truncatula root hair cells, by stimulation with lipochitinoligosaccharides specific for the induction of nodules (Nod-LCOs), or the interaction with mycorrhiza (Myc-LCOs). Intracellular micro electrodes were used, in combination with Ca2+ sensitive reporter dyes, to study the relations between cytosolic Ca2+ signals and membrane potential changes. We found that sulfated Myc- as well as Nod-LCOs initiate a membrane depolarization, which depends on the chemical composition of these signaling molecules, as well as the genotype of the plants that were studied. A successive application of sulfated Myc-LCOs and Nod-LCOs resulted only in a single transient depolarization, indicating that Myc-LCOs can repress plasma membrane responses to Nod-LCOs. In contrast to current models, the Nod-LCO-induced depolarization precedes changes in the cytosolic Ca2+ level of root hair cells. The Nod-LCO induced membrane depolarization thus is most likely independent of cytosolic Ca2+ signals and nuclear Ca2+ spiking.
Highlights
Roots establish two symbiotic associations with microbes that both play an important role in plant nutrition
The membrane potential depolarization of root hair cells represents one of the first steps evoked by Nod-LCOs in the host plants [28,29,30], but it is unknown if this response is provoked by Myc-LCOs
We tested the impact of a Sinorhizobium meliloti Nod-LCO (NodSM-IV, C16:2, S), on the membrane potential of M. truncatula roots using the micro electrode impalement technique (Fig 1A)
Summary
Roots establish two symbiotic associations with microbes that both play an important role in plant nutrition. An ancient symbiosis with Arbuscular Mycorrhizal fungi (AM) is found in approximately 80% of land plants, which evolved roughly 450 million years ago [1, 2]. The Root Nodule Symbiosis (RNS) emerged only within the last 60 million years and is confined to the family of legume plants (Fabaceae) with the exception of Parasponia (Cannabaceae) [3, 4]. AM and RNS are of great importance for plant nutrition, as AM fungi supply plants with various nutrients from the soil [5], whereas the rhizobium bacteria in the nodules provide fixed nitrogen sources [6, 7]. AM fungi and nitrogen-fixing bacteria exudate diffusible symbiotic signals, consisting of a chitinoligosaccharide
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