Lotus/enzymology; Mesorhizobium/physiology; Plant Proteins/metabolism; Protein Kinases/metabolism; Root Nodules, Plant/microbiology; Symbiosis/physiology; Amino Acid Motifs; Amino Acid Sequence; Amino Acid Substitution; Arabidopsis/genetics; Arabidopsis Proteins/genetics; Arabidopsis Proteins/metabolism; Chitin/metabolism; Evolution, Molecular; Gene Expression Profiling; Gene Expression Regulation, Plant/physiology; Genetic Complementation Test; Lipopolysaccharides/metabolism; Lotus/genetics; Lotus/microbiology; Mesorhizobium/genetics; Molecular Sequence Data; Nitrogen Fixation/physiology; Plant Proteins/genetics; Plants, Genetically Modified; Protein Kinases/chemistry; Protein Kinases/genetics; Protein Serine-Threonine Kinases/genetics; Protein Serine-Threonine Kinases/metabolism; Protein Structure, Tertiary; Receptors, Cell Surface/genetics; Receptors, Cell Surface/metabolism; Root Nodules, Plant/cytology; Root Nodules, Plant/metabolism; Sequence Alignment; Signal Transduction; Symbiosis/genetics