Abstract
Receptor(-like) kinases with Lysin Motif (LysM) domains in their extracellular region play crucial roles during plant interactions with microorganisms; e.g. Arabidopsis thaliana CERK1 activates innate immunity upon perception of fungal chitin/chitooligosaccharides, whereas Medicago truncatula NFP and LYK3 mediate signalling upon perception of bacterial lipo-chitooligosaccharides, termed Nod factors, during the establishment of mutualism with nitrogen-fixing rhizobia. However, little is still known about the exact activation and signalling mechanisms of MtNFP and MtLYK3. We aimed at investigating putative molecular interactions of MtNFP and MtLYK3 produced in Nicotiana benthamiana. Surprisingly, heterologous co-production of these proteins resulted in an induction of defence-like responses, which included defence-related gene expression, accumulation of phenolic compounds, and cell death. Similar defence-like responses were observed upon production of AtCERK1 in N. benthamiana leaves. Production of either MtNFP or MtLYK3 alone or their co-production with other unrelated receptor(-like) kinases did not induce cell death in N. benthamiana, indicating that a functional interaction between these LysM receptor-like kinases is required for triggering this response. Importantly, structure-function studies revealed that the MtNFP intracellular region, specific features of the MtLYK3 intracellular region (including several putative phosphorylation sites), and MtLYK3 and AtCERK1 kinase activity were indispensable for cell death induction, thereby mimicking the structural requirements of nodulation or chitin-induced signalling. The observed similarity of N. benthamiana response to MtNFP and MtLYK3 co-production and AtCERK1 production suggests the existence of parallels between Nod factor-induced and chitin-induced signalling mediated by the respective LysM receptor(-like) kinases. Notably, the conserved structural requirements for MtNFP and MtLYK3 biological activity in M. truncatula (nodulation) and in N. benthamiana (cell death induction) indicates the relevance of the latter system for studies on these, and potentially other symbiotic LysM receptor-like kinases.
Highlights
Legumes can establish a mutualism with compatible rhizobia leading to nodulation, i.e. a formation of specialized symbiotic organs in which atmospheric dinitrogen is converted into ammonia by the bacteria in exchange for plant carbohydrates
M. truncatula (Medicago)Nod Factor Perception (MtNFP) and MtLYK3 cDNA sequences were fused at their 39 ends to the sequence encoding a fluorescent protein (FP); either a super yellow fluorescent protein 2 or mCherry [43,44], and were expressed from a CaMV 35S promoter in Nicotiana leaves, where they were delivered by Agrobacterium-mediated transformation
Confocal laser-scanning microscopy analysis demonstrated co-localization of both MtNFP-super yellow fluorescent protein 2 (sYFP2) and MtLYK3sYFP2 fusions with a plasma membrane (PM) marker, indicating PM localization of MtNFP and MtLYK3 fusions in Nicotiana leaf epidermal cells
Summary
Legumes can establish a mutualism with compatible rhizobia leading to nodulation, i.e. a formation of specialized symbiotic organs (nodules) in which atmospheric dinitrogen is converted into ammonia by the bacteria in exchange for plant carbohydrates. Nod factors (NFs) play a central role during most Rhizobium-legume (RL) symbioses [1]. They are secreted rhizobial signals whose perception by host legume roots is required for root nodule organogenesis, invasion of rhizobia toward a nodule primordium, and accommodation of bacteria inside nodule cells [2,3,4]. LjNFR1, LjNFR5, MtNFP, and an additional Medicago gene, LysM domain-containing Receptor-Like Kinase/Root Hair Curling (MtLYK3/ MtHCL), are required for rhizobial infection via so-called infection threads through which the bacteria penetrate nodule primordia [9,12,13,14,15]. Demonstrated binding of NF derivatives to LjNFR1 and LjNFR5 confirmed their role as NF receptors [19], whereas the exact mechanism of MtNFP and MtLYK3 activation by compatible NFs remains to be shown
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
