Functions of the respiratory burst oxidase in biotic interactions, abiotic stress and development

The production of reactive oxygen intermediates (ROI) is among the earliest temporal events following pathogen recognition in plants. Initially, ROI were thought to be cell-death executioners. Emerging evidence, however, suggests a broader role for ROI as signals that mediate responses to infection, the abiotic environment, developmental cues, and programmed cell death in different cell types. The Respiratory burst oxidase homolog (Rboh) gene family encodes the key enzymatic subunit of the plant NADPH oxidase. Rboh proteins are the source of ROI produced following pathogen recognition and in a variety of other processes.     

Characterization of MDGA1, a novel human glycosylphosphatidylinositol-anchored protein localized in lipid rafts

We report the characterization of the novel human protein MDGA1 encoded by MDGA1 (MAM domain containing glycosylphosphatidylinositol anchor-1) gene, firstly termed as GPIM. MDGA1 has been mapped to 6p21 and it is expressed in human tissues and tumors. The deduced polypeptide consists of 955 amino acids and exhibits structural features found in different types of cell adhesion molecules (CAMs), such as the presence of both immunoglobulin domains and a MAM domain or the capacity to anchor to the cell membrane by a GPI (glycosylphosphatidylinositol) motif. Our results demonstrate that human MDGA1 (hMDGA1) is localized in the membrane of eukaryotic cells. The protein follows the secretion pathway and finally it is retained in the cell membrane by a GPI anchor, susceptible to be cleavaged by phospholipase C (PI-PLC). Moreover, our results reveal that hMDGA1 is localized specifically into membrane microdomains known as lipid rafts. Finally, as other proteins of the secretory pathway, hMDGA1 undergoes other post-translational modification consisting of N-glycosylation.     

Functional properties of the p33 and p55 domains of the Helicobacter pylori vacuolating cytotoxin

Helicobacter pylori secretes an 88-kDa vacuolating cytotoxin (VacA) that may contribute to the pathogenesis of peptic ulcer disease and gastric cancer. VacA cytotoxic activity requires assembly of VacA monomers into oligomeric structures, formation of anion-selective membrane channels, and entry of VacA into host cells. In this study, we analyzed the functional properties of recombinant VacA fragments corresponding to two putative VacA domains (designated p33 and p55). Immunoprecipitation experiments indicated that these two domains can interact with each other to form protein complexes. In comparison to the individual VacA domains, a mixture of the p33 and p55 proteins exhibited markedly enhanced binding to the plasma membrane of mammalian cells. Furthermore, internalization of the VacA domains was detected when cells were incubated with the p33/p55 mixture but not when the p33 and p55 proteins were tested individually. Incubation of cells with the p33/p55 mixture resulted in cell vacuolation, whereas the individual domains lacked detectable cytotoxic activity. Interestingly, sequential addition of p55 followed by p33 resulted in VacA internalization and cell vacuolation, whereas sequential addition in the reverse order was ineffective. These results indicate that both the p33 and p55 domains contribute to the binding and internalization of VacA and that both domains are required for vacuolating cytotoxic activity. Reconstitution of toxin activity from two separate domains, as described here for VacA, has rarely been described for pore-forming bacterial toxins, which suggests that VacA is a pore-forming toxin with unique structural properties.     

Molecular and morphological phylogenetic analysis of Brachiaria and Urochloa (Poaceae)

The taxonomic relationships of Brachiaria and Urochloa have been questioned based on previous morphological studies. In this paper, we reconsider the phylogenetic relationships of these genera using 22 species of Brachiaria and Urochloa and six species of Paniceae as out-groups. The ITS1, 5.8S, and ITS2 region (internal transcribed spacer) of nuclear ribosomal DNA and eight morphological characters of the inflorescence were compiled into a data matrix. The cladistic analyses suggest that Urochloa-Brachiaria as a complex is paraphyletic with Eriochloa and Melinis. Species of all these genera share molecular synapomorphies and belong to the same monophyletic groups. The results confirm the continuous gradation between those genera previously found in several morphological studies. Therefore, the following eight new combinations are made: Urochloa bovonei (Chiov.) A.M. Torres & C.M. Morton, Urochloa dura (Stapf) A.M. Torres & C.M. Morton, Urochloa dura var. dura (Stapf) A.M. Torres & C.M. Morton, Urochloa dura var. pilosa (J.G. Anderson) A.M. Torres & C.M. Morton, Urochloa lachnantha (Hochst.) A.M. Torres & C.M. Morton, Urochloa leersioides (Hochst.) A.M. Torres & C.M. Morton, Urochloa nigropedata (Munro ex Ficalho & Hiern) A.M. Torres & C.M. Morton, and Urochloa subulifolia (Mez) A.M. Torres & C.M. Morton.     

Proteomic analysis of soybean root hairs after infection by Bradyrhizobium japonicum

Infection of soybean root hairs by Bradyrhizobium japonicum is the first of several complex events leading to nodulation. In the current proteomic study, soybean root hairs after inoculation with B. japonicum were separated from roots. Total proteins were analyzed by two-dimensional (2-D) polyacrylamide gel electrophoresis. In one experiment, 96 protein spots were analyzed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) to compare protein profiles between uninoculated roots and root hairs. Another 37 spots, derived from inoculated root hairs over different timepoints, were also analyzed by tandem MS (MS/MS). As expected, some proteins were differentially expressed in root hairs compared with roots (e.g., a chitinase and phosphoenolpyruvate carboxylase). Out of 37 spots analyzed by MS/MS, 27 candidate proteins were identified by database comparisons. These included several proteins known to respond to rhizobial inoculation (e.g., peroxidase and phenylalanine-ammonia lyase). However, novel proteins were also identified (e.g., phospholipase D and phosphoglucomutase). This research establishes an excellent system for the study of root-hair infection by rhizobia and, in a more general sense, the functional genomics of a single, plant cell type. The results obtained also indicate that proteomic studies with soybean, lacking a complete genome sequence, are practical.     

The gene ENHANCER OF PINOID controls cotyledon development in the Arabidopsis embryo

During Arabidopsis embryo development, cotyledon primordia are generated at transition stage from precursor cells that are not derived from the embryonic shoot apical meristem (SAM). To date, it is not known which genes specifically instruct these precursor cells to elaborate cotyledons, nor is the role of auxin in cotyledon development clear. In laterne mutants, the cotyledons are precisely deleted, yet the hypocotyl and root are unaffected. The laterne phenotype is caused by a combination of two mutations: one in the PINOID (PID) gene and another mutation in a novel locus designated ENHANCER OF PINOID (ENP). The expression domains of shoot apex organising genes such as SHOOT MERISTEMLESS (STM) extend along the entire apical region of laterne embryos. However, analysis of pid enp stm triple mutants shows that ectopic activity of STM does not appear to cause cotyledon obliteration. This is exclusively caused by enp in concert with pid. In pinoid embryos, reversal of polarity of the PIN1 auxin transport facilitator in the apex is only occasional, explaining irregular auxin maxima in the cotyledon tips. By contrast, polarity of PIN1:GFP is completely reversed to basal position in the epidermal layer of the laterne embryo. Consequently auxin, which is believed to be essential for organ formation, fails to accumulate in the apex. This strongly suggests that ENP specifically regulates cotyledon development through control of PIN1 polarity in concert with PID.     

BAS1 and SOB7 act redundantly to modulate Arabidopsis photomorphogenesis via unique brassinosteroid inactivation mechanisms

Active brassinosteroids (BRs), such as brassinolide (BL) and castasterone (CS), are growth-promoting plant hormones. An Arabidopsis cytochrome P450 monooxygenase (CYP734A1, formerly CYP72B1), encoded by the BAS1 gene, inactivates BRs and modulates photomorphogenesis. BAS1 was identified as the overexpressed gene responsible for a dominant, BR-deficient mutant, bas1-D. This mutant was isolated in an activation-tagged screen designed to identify redundant genes that might not be identified in classic loss-of-function screens. Here we report the isolation of a second activation-tagged mutant with a BR-deficient phenotype. The mutant phenotype is caused by the overexpression of SOB7 (CYP72C1), a homolog of BAS1. We generated single and double null-mutants of BAS1 and SOB7 to test the hypothesis that these two genes act redundantly to modulate photomorphogenesis. BAS1 and SOB7 act redundantly with respect to light promotion of cotyledon expansion, repression of hypocotyl elongation and flowering time in addition to other phenotypes not regulated by light. We also provide biochemical evidence to suggest that BAS1 and SOB7 act redundantly to reduce the level of active BRs, but have unique mechanisms. Overexpression of SOB7 results in a dramatic reduction in endogenous CS levels, and although single null-mutants of BAS1 and SOB7 have the same level of CS as the wild type, the double null-mutant has twice the amount. Application of BL to overexpression lines of BAS1 or SOB7 results in enhanced metabolism of BL, though only BAS1 overexpression lines confer enhanced conversion to 26-OHBL, suggesting that SOB7 and BAS1 convert BL and CS into unique products.     

Surimi wash water treatment for protein recovery: effect of chitosan-alginate complex concentration and treatment time on protein adsorption

Chitosan (Chi), a protein recovery agent for the treatment of aqueous food processing streams, appears to work by mechanical entrapment and electrostatic interaction of chitosan amino groups with anionic groups on proteins. Chitosan effectiveness for recovering soluble proteins from surimi wash water (SWW) is increased by complexation with alginate (Alg) and by adjusting complex concentration and treatment time. Flocculation at 20 degrees C with Chi-Alg at a 0.2 mixing ratio added as 20, 40, 100 and 150 mg/L SWW was aided by 5 min agitation at 130 rpm and then held at the same temperature for 30 min, 1 and 24 h. Turbidity measurements, protein determinations and qualitative FTIR analysis confirmed SWW protein adsorption which depended on Chi-Alg concentration and reaction time while turbidity reduction was affected by concentration only. No differences (p < 0.05) in protein adsorption were found between 1 and 24 h. Using 100 mg Chi-Alg complex/L SWW for 1 h achieved 83% protein adsorption and 97% turbidity reduction.