Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2007
Publication Date: 4/20/2007
Citation: Zhang, X., Wu, X., Findley, S., Wan, J., Libault, M., Nguyen, H.T., Cannon, S.B. 2007. Molecular evolution of lysin motif-type receptor-like kinases in plants. Plant Physiology. 144:623-636.
Interpretive Summary: One of the most important biological "marriages" in the plant world involves the "Rhizobium" bacteria that can convert atmospheric nitrogen gas into a form of nitrogen that can be used directly by plants as fertilizer. The "legume" plant family (including peas, clovers, beans, and many shrubs and tropical trees) has unique structures ("nodules") that develop on the roots. Nodules host Rhizobial bacteria, which in turn provide nitrogen fertilizer to the plant. This association provides the largest source of natural nitrogen fertilizer in every ecosystem. How did that relationship evolve, and what might be required to establish this relationship in other crop plants? One of the first steps will be to understand how the plant recognizes the presence of the bacterium outside of the roots. Other papers have determined that the legume "LysM" protein is responsible for percieving the bacterium. This paper investigates how this protein (and the underlying gene) may have evolved in the legume plant family, and in soybeans in particular. The main finding: LysM gene is ancient (is found in every organismal kingdom), but a key event leading to the new function in legume plants may have been the duplication of this gene early in the evolution of this plant family. This research benefits scientists investigating nitrogen fixation, ultimately this research benefits soybean growers.
Technical Abstract: The lysin motif (LysM) domain is an ancient and ubiquitous protein module that binds peptidoglycan and structurally related molecules. A genomic survey in a large number of species spanning all kingdoms reveals that the combination of LysM and receptor kinase domains is present exclusively in plants. However, the particular biological functions and molecular evolution of this gene family remain largely unknown. We show that LysM domains in plant LysM proteins are highly diversified and that a minimum of six distinct types of LysM motifs exist in plant LysM kinase proteins and five additional types of LysM motifs exist in nonkinase plant LysM proteins. Further, motif similarities suggest that plant LysM motifs are ancient. Although phylogenetic signals are not sufficient to resolve the earliest relationships, plant LysM motifs may have arisen through common ancestry with LysM motifs in other kingdoms. Within plants, the gene family has evolved through local and segmental duplications. The family has undergone further duplication and diversification in legumes, where some LysM kinase genes function as receptors for bacterial nodulation factor. Two pairs of homeologous regions were identified in soybean (Glycine max) based on microsynteny and fluorescence in situ hybridization. Expression data show that most plant LysM kinase genes are expressed predominantly in the root and that orthologous LysM kinase genes share similar tissue expression patterns. We also examined synteny around plant LysM kinase genes to help reconstruct scenarios for the evolution of this important gene family.