ABSTRACT
Functional divergence of paralogs following gene duplication is one of the mechanisms leading to evolution of novel pathways and traits. Here we show that divergence of Lys11 and Nfr5 LysM receptor kinase paralogs of Lotus japonicus has affected their specificity for lipochitooligosaccharides (LCOs) decorations, while the innate capacity to recognize and induce a downstream signalling after perception of rhizobial LCOs (Nod factors) was maintained. Regardless of this conserved ability, Lys11 was found neither expressed, nor essential during nitrogen-fixing symbiosis, providing an explanation for the determinant role of Nfr5 gene during Lotus-rhizobia interaction. Lys11 was expressed in root cortex cells associated with intraradical colonizing arbuscular mycorrhizal fungi. Detailed analyses of lys11 single and nfr1nfr5lys11 triple mutants revealed a functional arbuscular mycorrhizal symbiosis, indicating that Lys11 alone, or its possible shared function with the Nod factor receptors is not essential for the presymbiotic phases of AM symbiosis. Hence, both subfunctionalization and specialization appear to have shaped the function of these paralogs where Lys11 acts as an AM-inducible gene, possibly to fine-tune later stages of this interaction.
Subject(s)
Lipopolysaccharides/metabolism , Lotus/microbiology , Mycorrhizae/physiology , Plant Proteins/metabolism , Plant Roots/microbiology , Amino Acid Sequence , Carbohydrate Sequence , Gene Expression Profiling/methods , Gene Expression Regulation, Plant , Host-Pathogen Interactions , Lotus/genetics , Mutation , Plant Proteins/genetics , Plant Roots/genetics , Plants, Genetically Modified , Rhizobium/physiology , Sequence Homology, Amino Acid , SymbiosisABSTRACT
Surface polysaccharides are important for bacterial interactions with multicellular organisms, and some are virulence factors in pathogens. In the legume-rhizobium symbiosis, bacterial exopolysaccharides (EPS) are essential for the development of infected root nodules. We have identified a gene in Lotus japonicus, Epr3, encoding a receptor-like kinase that controls this infection. We show that epr3 mutants are defective in perception of purified EPS, and that EPR3 binds EPS directly and distinguishes compatible and incompatible EPS in bacterial competition studies. Expression of Epr3 in epidermal cells within the susceptible root zone shows that the protein is involved in bacterial entry, while rhizobial and plant mutant studies suggest that Epr3 regulates bacterial passage through the plant's epidermal cell layer. Finally, we show that Epr3 expression is inducible and dependent on host perception of bacterial nodulation (Nod) factors. Plant-bacterial compatibility and bacterial access to legume roots is thus regulated by a two-stage mechanism involving sequential receptor-mediated recognition of Nod factor and EPS signals.
Subject(s)
Lipopolysaccharides/metabolism , Lotus/metabolism , Lotus/microbiology , Plant Proteins/metabolism , Receptors, Cell Surface/metabolism , Rhizobium/metabolism , Symbiosis , Amino Acid Sequence , Carbohydrate Sequence , Lipopolysaccharides/chemistry , Lotus/genetics , Molecular Sequence Data , Mutation/genetics , Phenotype , Plant Epidermis/metabolism , Plant Epidermis/microbiology , Plant Proteins/chemistry , Plant Proteins/genetics , Plant Root Nodulation , Protein Kinases/chemistry , Protein Kinases/genetics , Protein Kinases/metabolism , Protein Structure, Tertiary , Receptors, Cell Surface/chemistry , Receptors, Cell Surface/genetics , Root Nodules, Plant/metabolism , Root Nodules, Plant/microbiology , Signal Transduction , Species Specificity , Suppression, Genetic/geneticsABSTRACT
The review sums up the long experience of the authors and other researchers in studying the genetic system of garden pea (Pisum sativum L.), which controls sthe development of nitrogen-fixing symbiosis and arbuscular mycorrhiza. A justified phenotypic classification of pea mutants is presented. Progress in identifying and cloning symbiotic genes is adequately reflected. The feasibility of using double inoculation as a means of increasing the plant productivity is demonstrated, in which the potential of a tripartite symbiotic system (pea plants-root nodule bacteria-arbuscular mycorrhiza) is mobilized.