Duplication and diversification of lectin receptor-like kinases (LecRLK) genes in soybean.

Lectin receptor-like kinases (LecRLKs) play important roles in plant development and stress responses. Although genome-wide studies of LecRLKs have been performed in several species, a comprehensive analysis including evolutionary, structural and functional analysis has not been carried out in soybean (Glycine max). In this study, we identified 185 putative LecRLK genes in the soybean genome, including 123 G-type, 60 L-type and 2 C-type LecRLK genes. Tandem duplication and segmental duplication appear to be the main mechanisms of gene expansion in the soybean LecRLK (GmLecRLK) gene family. According to our phylogenetic analysis, G-type and L-type GmLecRLK genes can be organized into fourteen and eight subfamilies, respectively. The subfamilies within the G-type GmLecRLKs differ from each other in gene structure and/or protein domains and motifs, which indicates that the subfamilies have diverged. The evolution of L-type GmLecRLKs has been more conservative: most genes retain the same gene structures and nearly the same protein domain and motif architectures. Furthermore, the expression profiles of G-type and L-type GmLecRLK genes show evidence of functional redundancy and divergence within each group. Our results contribute to a better understanding of the evolution and function of soybean LecRLKs and provide a framework for further functional investigation of them.

Knights in action: lectin receptor-like kinases in plant development and stress responses.

The Receptor-Like Kinase (RLK) is a vast protein family with over 600 genes in Arabidopsis and 1100 in rice. The Lectin RLK (LecRLK) family is believed to play crucial roles in saccharide signaling as well as stress perception. All the LecRLKs possess three domains: an N-terminal lectin domain, an intermediate transmembrane domain, and a C-terminal kinase domain. On the basis of lectin domain variability, LecRLKs have been subgrouped into three subclasses: L-, G-, and C-type LecRLKs. While the previous studies on LecRLKs were dedicated to classification, comparative structural analysis and expression analysis by promoter-based studies, most of the recent studies on LecRLKs have laid special emphasis on the potential of this gene family in regulating biotic/abiotic stress and developmental pathways in plants, thus making the prospects of studying the LecRLK-mediated regulatory mechanism exceptionally promising. In this review, we have described in detail the LecRLK gene family with respect to a historical, evolutionary, and structural point of view. Furthermore, we have laid emphasis on the LecRLKs roles in development, stress conditions, and hormonal response. We have also discussed the exciting research prospects offered by the current knowledge on the LecRLK gene family. The multitude of the LecRLK gene family members and their functional diversity mark these genes as both interesting and worthy candidates for further analysis, especially in the field of crop improvement.

Extended and bent conformations of the mannose receptor family.

In mammals, the mannose receptor family consists of four members, Endo180, DEC-205, phospholipase A2 receptor and the mannose receptor. The extracellular domains of all these receptors contain a similar arrangement of domains in which an N-terminal cysteine-rich domain is followed by a single fibronectin type II domain and eight or ten C-type lectin-like domains. This review focuses on the three-dimensional structure of the receptors in the mannose receptor family and its functional implication. Recent research has revealed that several members of this family can exist in at least two configurations: an extended conformation with the N-terminal cysteine-rich domain pointing outwards from the cell membrane and a bent conformation where the N-terminal domains fold back to interact with C-type lectin-like domains at the middle of the structure. Conformational transitions between these two states seem to regulate the interaction of these receptors with ligands and their oligomerization.

Expression of high affinity receptors for murine interleukin 4 (BSF-1) on hemopoietic and nonhemopoietic cells.

In this report a method for the affinity purification and radiolabeling of recombinant mouse interleukin (IL)-4 is described. It is shown on the basis of several criteria that IL-4 retains full biologic activity after radioiodination and can therefore be used as a valid model for measuring the binding characteristics of native IL-4. By using Scatchard plot analysis of equilibrium binding data, it is demonstrated that 125I-IL-4 binds to a high affinity cell surface receptor which is expressed by both hemopoietic and nonhemopoietic cells. The dissociation constant for 125I-IL-4 (Kd = 20 to 60 pM) corresponds to the concentration of IL-4 which gives 50% biologic activity (i.e., 10 to 30 pM). Binding of 125I-IL-4 is rapid (t1/2 of 2 min), whereas dissociation occurs at a slow rate (t1/2 approximately 4 hr). The IL-4 receptor shows a high degree of specificity. Whereas unlabeled mouse IL-4 competed with mouse 125I-IL-4 in an equimolar fashion for binding to IL-4 receptors, several other lymphokines, including mouse IL-2, IL-3, interferon-gamma, granulocyte-macrophage colony-stimulating factor, and human IL-1, IL-2, and IL-4 were unable to inhibit, even at molar excesses of 400 to 800-fold. At 37 degrees C, 125I-IL-4 is rapidly internalized (approximately 200 molecules/cell/min) by HT-2 cells, with at least 85% of cell surface receptors being functional in this respect. Receptors for IL-4 were found to be expressed by subclasses of T and B cells, mast cells, macrophages, and by cells of the myeloid and erythroid lineages. This wide distribution of receptor expression closely matches the known spectrum of biologic activities of IL-4, including proliferation and/or differentiation of T and B cells, mast cells and granulocytes, and induction of macrophage antigen-presenting capacity. IL-4 receptors were also found on a variety of nonhemopoietic cells such as cloned stromal cell lines from the bone marrow, spleen, thymus, and brain, and on muscle, brain, melanoma, fibroblast, and liver cells. Indeed, only 5 of more than 90 cell types tested have undetectable numbers of IL-4 receptors. The biologic effects of IL-4 on nonhemopoietic cells have not yet been reported and await elucidation.

Distribution of anionic sites and glycoconjugates on the endothelial surfaces of the developing blood-brain barrier.

The distribution of anionic sites detected in vitro with cationized ferritin and lectin-binding sites on the endothelial cell (EC) surface of brain micro-blood vessels was studied by electron microscopy. Gold-labeled lectins and glycoproteins and Lowicryl K4M-embedded brain samples obtained from mouse embryos (19th day), and from 1-, 5-, 12-, 24- and 48-day-old and adult mice were used. It was shown that the functional maturation of the blood-brain barrier (BBB) occurring in the mouse after birth between the 12th and 24th day of life is accompanied by a disappearance of vesicular transport in capillaries and by the formation of a uniform, thin, negatively charged layer on the surface of the EC. Concomitantly the binding of lectins specific for beta-D-galactosyl (RCA) and sialyl (LFA and WGA) residues become progressively more intense and uniform on both luminal and abluminal fronts of the EC. The concentration of HPA-binding sites on the abluminal side of the EC and in the basement membrane increases. Similarly the binding of Con A becomes more intense on abluminal than on luminal front of the EC. These observations suggest that extensive remodeling of anionic sites and surface glycoprotein layer and also the elaboration of ECs polarity occur during BBB maturation.

Lectin binding sites on human endocervix: a comparison with secretory and proliferative endometrium.

Endocervix and corresponding endometrium of women of reproductive age were studied histochemically with 13 fluorescein isothiocyanate-labeled lectins to delineate the differences between the epithelial cells in two anatomical sites. Lectin from Maclura pomifera (MPA), Ulex europaeus (UEA-I), Glycine max (SBA), and Vicia villosa (VVA) bound only to endocervical epithelium and were the only four lectins that distinguished endocervical from endometrial epithelium. These differences were independent of menstrual cyclic changes and blood group antigen secretion. These data show that lectins can be used to histochemically distinguish endocervical from endometrial glands.