Transcriptional behavior of EUL-related rice lectins toward important abiotic and biotic stresses.

The rice genome encodes several genes for putative carbohydrate-binding proteins belonging to the family of Euonymus related lectins (EULs). This lectin family was discovered recently and evidence shows that the expression of these proteins is subject to multiple environmental stresses. In this study, quantitative reverse transcription PCR (qRT-PCR) was conducted on rice seedlings exposed to various abiotic (150mM NaCl, 100mM mannitol, and 100μM abscisic acid (ABA)) and biotic (Xanthomonas oryzae pv.

Promiscuity of the euonymus carbohydrate-binding domain.

Plants synthesize small amounts of carbohydrate-binding proteins on exposure to stress. For example, on exposure to drought, high salt, wounding and by treatment with some plant hormones or by pathogen attack. In contrast to the 'classical' plant lectins that are mostly located in the vacuolar compartment, this new class of inducible lectins is present in the cytoplasm and in the nucleus.

Lectin activity of the nucleocytoplasmic EUL protein from Arabidopsis thaliana.

The Euonymus lectin (EUL) domain was recognized as the structural motif for a novel class of putative carbohydrate binding proteins. Confocal microscopy demonstrated that the lectin from Euonymus europaeus (EEA) as well as the EUL protein from Arabidopsis thaliana (ArathEULS3) are located in the nucleocytoplasmic compartment of the plant cell. ArathEULS3 as well as its EUL domain were successfully expressed in Pichia pastoris and purified.

Expression analysis of the nucleocytoplasmic lectin 'Orysata' from rice in Pichia pastoris.

The Oryza sativa lectin, abbreviated Orysata, is a mannose-specific, jacalin-related lectin expressed in rice plants after exposure to certain stress conditions. Expression of a fusion construct containing the rice lectin sequence linked to enhanced green fluorescent protein in Bright Yellow 2 tobacco cells revealed that Orysata is located in the nucleus and the cytoplasm of the plant cell, indicating that it belongs to the class of nucleocytoplasmic jacalin-related lectins. Since the expression level of Orysata in rice tissues is very low the lectin was expressed in the methylotrophic yeast Pichia pastoris with the Saccharomyces α-factor sequence to direct the recombinant protein into the secretory pathway and express the protein into the medium.

Differences in the mannose oligomer specificities of the closely related lectins from Galanthus nivalis and Zea mays strongly determine their eventual anti-HIV activity.

Background: In a recent report, the carbohydrate-binding specificities of the plant lectins Galanthus nivalis (GNA) and the closely related lectin from Zea mays (GNAmaize) were determined by glycan array analysis and indicated that GNAmaize recognizes complex-type N-glycans whereas GNA has specificity towards high-mannose-type glycans. Both lectins are tetrameric proteins sharing 64% sequence similarity.

Results: GNAmaize appeared to be ~20- to 100-fold less inhibitory than GNA against HIV infection, syncytia formation between persistently HIV-1-infected HuT-78 cells and uninfected CD4+ T-lymphocyte SupT1 cells, HIV-1 capture by DC-SIGN and subsequent transmission of DC-SIGN-captured virions to uninfected CD4+ T-lymphocyte cells.

Identical homologs of the Galanthus nivalis agglutinin in Zea mays and Fusarium verticillioides.

The structural domain corresponding to the Galanthus nivalis agglutinin (GNA) is a mannose-binding motif that was originally discovered in plants but according to recent data also occurs in other eukaryotes and prokaryotes. Transcriptome analyses revealed that Fusarium verticillioides expresses a protein (FvGLLc1) identical to a recently identified cytoplasmic/nuclear GNA-like lectin from maize (ZmGLLc). The FvGLLc1 and ZmGLLc gene sequences are nearly identical in the coding region as well as in the intron and the 5 and 3 prime untranslated regions.

Proteins with an Euonymus lectin-like domain are ubiquitous in Embryophyta.

Background: Cloning of the Euonymus lectin led to the discovery of a novel domain that also occurs in some stress-induced plant proteins. The distribution and the diversity of proteins with an Euonymus lectin (EUL) domain were investigated using detailed analysis of sequences in publicly accessible genome and transcriptome databases.

Results: Comprehensive in silico analyses indicate that the recently identified Euonymus europaeus lectin domain represents a conserved structural unit of a novel family of putative carbohydrate-binding proteins, which will further be referred to as the Euonymus lectin (EUL) family.

Related lectins from snowdrop and maize differ in their carbohydrate-binding specificity.

Searches in an EST database from maize revealed the expression of a protein related to the Galanthus nivalis (GNA) agglutinin, referred to as GNA(maize). Heterologous expression of GNA(maize) in Pichia pastoris allowed characterization of the first nucleocytoplasmic GNA homolog from plants. GNA(maize) is a tetrameric protein which shares 64% sequence similarity with GNA.

The "old" Euonymus europaeus agglutinin represents a novel family of ubiquitous plant proteins.

Molecular cloning of the "old" but still unclassified Euonymus europaeus agglutinin (EEA) demonstrated that the lectin is a homodimeric protein composed of 152 residue subunits. Analysis of the deduced sequence indicated that EEA is synthesized without a signal peptide and undergoes no posttranslational processing apart from the removal of a six-residue N-terminal peptide. Glycan array screening confirmed the previously reported high reactivity of EEA toward blood group B oligosaccharides but also revealed binding to high mannose N-glycans, providing firm evidence for the occurrence of a plant carbohydrate-binding domain that can interact with structurally different glycans.

Localization and topogenesis studies of cytoplasmic and vacuolar homologs of the Galanthus nivalis agglutinin.

The Galanthus nivalis agglutinin (GNA) is synthesized as a preproprotein. To corroborate the role of the different targeting peptides in the topogenesis of GNA and related proteins, different constructs were made whereby both the complete original GNA gene and different truncated sequences were coupled to the enhanced green fluorescent protein (EGFP). In addition, a GNA ortholog from rice that lacks the signal peptide and C-terminal propeptide sequence was fused to EGFP.

The liverwort Marchantia polymorpha expresses orthologs of the fungal Agaricus bisporus agglutinin family.

A lectin different from the previously described mannose-binding agglutinins has been isolated from the liverwort Marchantia polymorpha. Biochemical characterization of the purified lectin combined with the data from earlier transcriptome analyses demonstrated that the novel M. polymorpha agglutinin is not related to any of the known plant lectin families, but closely resembles the Agaricus bisporus-type lectins, which hitherto have been found exclusively in fungi.

The identification of inducible cytoplasmic/nuclear carbohydrate-binding proteins urges to develop novel concepts about the role of plant lectins.

During the last few years compelling evidence has been presented for the occurrence of cytoplasmic/nuclear plant lectins that are not detectable in normal plants but are only induced upon application of well-defined stress conditions. Since both the regulation of the expression and the subcellular location indicate that these 'non-classical lectins' are good candidates to play a physiologically important role as mediators of specific protein-carbohydrate-interactions within the plant cell, a critical assessment is made of the impact of these findings on the development of novel concepts about the role of plant lectins. Based on an analysis of the biochemical, molecular and evolutionary data of a jasmonate-induced chitin-binding lectin from tobacco leaves and a salt/jasmonate-induced leaf lectin from rice it is concluded that these lectins most probably interact with endogenous glycans located within the cytoplasmic/nuclear compartment of the plant cell.