Role of defense/stress-related marker genes, proteins and secondary metabolites in defining rice self-defense mechanisms.

Rice, a first cereal crop whose draft genome sequence from two subspecies (japonica-type cv. Nipponbare and indica-type 93-11) was available in 2002, along with its almost complete genome sequence in 2005, has drawn the attention of researchers worldwide because of its immense impact on human existence. One of the most critical research areas in rice is to discern the self-defense mechanism(s), an innate property of all living organisms. The last few decades have seen scattered research into rice responses to diverse environmental stimuli and stress factors. Our understanding on rice self-defense mechanism has increased considerably with accelerated research during recent years mainly due to identification and characterization of several defense/stress-related components, genes, proteins and secondary metabolites. As these identified components have been used to study the defense/stress pathways, their compilation in this review will undoubtedly help rice (and others) researchers to effectively use them as a potential marker for better understanding, and ultimately, in defining rice (and plant) self-defense response pathways.     

Role of anti-beta-glucan antibody in host defense against fungi

We have recently detected an anti-beta-glucan antibody in normal human and normal mouse sera. The anti-beta-glucan antibody showed reactivity to pathogenic fungal Aspergillus and Candida cell wall glucan. Anti-beta-glucan antibody could bind whole Candida cells. It also enhanced the candidacidal activity of macrophages in vitro. The anti-beta-glucan antibody titer of DBA/2 mice intravenously administered either Candida or Aspergillus solubilized cell wall beta-glucan decreased remarkably dependent on dose. Moreover, in deep mycosis patients, the anti-beta-glucan antibody titer decreased, and this change correlated with clinical symptoms and other parameters such as C-reactive protein. It was suggested that the anti-beta-glucan antibody formed an antigen-antibody complex and participated in the immune response as a molecule recognizing pathogenic fungi.     

Role of inflammasomes in host defense against Citrobacter rodentium infection

Citrobacter rodentium is an enteric bacterial pathogen of the mouse intestinal tract that triggers inflammatory responses resembling those of humans infected with enteropathogenic and enterohemorrhagic Escherichia coli. Inflammasome signaling is emerging as a central regulator of inflammatory and host responses to several pathogens, but the in vivo role of inflammasome signaling in host defense against C. rodentium has not been characterized. Here, we show that mice lacking the inflammasome components Nlrp3, Nlrc4, and caspase-1 were hypersusceptible to C. rodentium-induced gastrointestinal inflammation. This was due to defective interleukin (IL)-1β and IL-18 production given that il-1β(-/-) and il-18(-/-) mice also suffered from increased bacterial burdens and exacerbated histopathology. C. rodentium specifically activated the Nlrp3 inflammasome in in vitro-infected macrophages independently of a functional bacterial type III secretion system. Thus, production of IL-1β and IL-18 downstream of the Nlrp3 and Nlrc4 inflammasomes plays a critical role in host defense against enteric infections caused by C. rodentium.     

Role of antimicrobial peptides in host defense against mycobacterial infections

Worldwide, tuberculosis remains the most important infectious disease causing morbidity and death. Currently, at least one-third of the world's population is infected with Mycobacterium tuberculosis. In addition, the World Health Organization estimates that about 8-10 million new tuberculosis cases occur annually worldwide and this incidence is currently increasing. Moreover, multidrug-resistant tuberculosis has been increasing in incidence in many areas during the past decade. These situations underscore the importance of the development of new therapeutic agents against mycobacterial infectious diseases. In this article, it is review current progress in the understanding of antimicrobial peptides as potential candidates to develop an alternative/adjunct therapeutic strategy against tuberculosis. This immunoadjunctive therapy might be evaluated in the context of possible drug resistance. This review also summarizes the knowledge about the functions of antimicrobial peptides in the pulmonary innate host defense system and their role in mycobacterial infection, and at the same time outlines recent advances in our understanding of the combined effect of antimicrobial peptides and anti-tuberculosis drugs against intracellular mycobacteria. A concerted effort should now focus on the clinical application of antimicrobial peptides for their practical use.     

Ecological and biotechnological importance of secondary metabolites produced by coral-associated bacteria

Symbiotic relationships between corals and their associated micro-organisms are essential to maintain host homeostasis. Coral-associated bacteria (CAB) can have different beneficial roles in the coral metaorganism, such as metabolizing essential nutrients for the coral host and protecting the coral from pathogens. Many CAB exert these functions via secondary metabolites, which include antibacterial, antifouling, antitumour, antiparasitic and antiviral compounds. This review describes how analysis of CAB has led to the discovery of secondary metabolites with potential biotechnological applications. The most commonly found types of secondary metabolites, antimicrobial and antibiofilm compounds, are emphasized and described. Recently developed methods that can be applied to enhance the culturing of CAB from shallow-water reefs and the less-studied deep-sea coral reefs are also discussed. Last, we suggest how the combined use of meta-omics and innovative growth-diffusion techniques can vastly improve the discovery of novel compounds in coral environments.     

Role and genetic basis of specialised secondary metabolites in Trichoderma ecophysiology

Species of fungal genus Trichoderma are characterized by a versatile lifestyle, high adaptability to the changing environmental conditions and the ability to establish sophisticated interactions with other organisms. Due to their ability to antagonize plant pathogens and to elicit the plant defence responses against biotic/abiotic stresses, Trichoderma spp. are commonly used as commercially biopesticides and biofertilizers. The Trichoderma success in the rhizosphere is supported by a wide arsenal of specialised metabolites (SMs) providing morphological and physiological autoregulation, self-protection and facilitating fungal communication. This review aims to explore the roles of SMs in the biology of fungi, with special emphasis on the genus Trichoderma and on how divergence in the SMs genetic structure determine Trichoderma lifestyles. Trichoderma genomes are endowed with a high number of SMs biosynthetic genes, and understanding the genetic basis of their biosynthesis is crucial for determining the role of these metabolites in Trichoderma ecophysiology and for expanding their application in crop protection. Recent advances on the characterization of the Trichoderma SMs genetic inventory driven by computational biology are discussed.     

Pyrenomycetes and Loculoascomycetes as sources of secondary metabolites

Over 400 secondary metabolites have been reported from members of the Pyrenomycetes and the Loculoascomycetes. Among these, members of the Hypocreaceae, the Clavicipitaceae, the Xylariaceae, the Melanosporaceae, and the Sordariaceae in the Pyrenomycetes, and those of the Pleosporaceae and the Sporormlaceae in the Loculoascomycetes have been explored frequently; and representative secondary metabolites produced by these fungi are illustrated. Many of them are reported to be phytotoxic and some of them have antibacterial or antifungal activities. Only recently were the compounds tested in screens targeted for specific enzyme inhibitors or receptoragonists/antagonists. This group of fungi are attractive for screening for novel natural products because of the diversity of species and physiology.     

Role of autophagy in the host defense against Toxoplasma gondii in astrocytes

Autophagy has recently been implicated in the host defense against the intracellular protozoan pathogen, Toxoplasma gondii, a major opportunistic pathogen of the central nervous system in immunosuppressed individuals. In both IFNγ-activated macrophages and astrocytes, the p47 GTPases traffic to the T. gondii parasitophorous vacuole, followed by vacuolar disruption, parasite killing, and clearance of the dead parasites. In macrophages, it is relatively well established that autophagy is involved in parasite elimination and killing. The role of autophagy in parasite elimination in astrocytes, a dominant host cell in the central nervous system, is much less clear. Our studies indicate that in IFNγ-stimulated astrocytes, autophagy of disrupted vacuoles and/or dead parasites does not occur but rather that degradation of the parasite occurs in the host cytoplasm. However, recent studies indicate autophagy may be involved in the elimination of the degraded parasite material from the astrocyte host cell cytoplasm and suggest that autophagous removal of degraded parasite material may be necessary for survival of the host cell. Delivery of parasite antigen from the cytosol to the endolysosomal compartments in astrocytes is of importance as it suggests a pathway by which astrocytes could present Toxoplasma antigens via the MHC Class II pathway and function as an antigen-presenting cell for the parasite in the brain.     

Role of inhibitors of proteolytic enzymes in plant defense against phytopathogenic microorganisms

This review analyzes the literature on various mechanisms of proteolytic enzyme inhibitors involved in plant defense against attack by phytopathogenic microorganisms. The action of proteinase inhibitors from plants upon the enzymes from pathogenic microorganisms and viruses is reviewed. Considerable attention is given to the induction of proteinase inhibitors in plants in response to the invasion of pathogens. Some aspects of application of proteinase inhibitors in biotechnology for production of transgenic plants with enhanced resistance to diseases are discussed.Translated from Biokhimiya, Vol. 69, No. 11, 2004, pp. 1600–1606.Original Russian Text Copyright © 2004 by Valueva, Mosolov.     

Marine actinomycetes as a source of novel secondary metabolites

A set of 600 actinomycetes strains which were isolated from marine sediments from various sites in the Pacific and Atlantic Oceans were screened for the production of bioactive secondary metabolites. Marine streptomycete strains were found to be producers of well known chemically diverse antibiotics isolated from terrestrial streptomycetes, as in the case of marine Micromonospora strains. New marine members of the rare genus Verrucosispora seem to be a promising source for novel bioactive secondary metabolites as shown in the case of the abyssomicin producing strain AB-18-032.     

Lipopolysaccharide-binding protein of Bombyx mori participates in a hemocyte-mediated defense reaction against gram-negative bacteria

BmLBP is a lipopolysaccharide-binding protein in B. mori and participates in bacterial clearance in vivo. Here, we investigated the function of BmLBP more specifically. More than 90% of injected gram-negative rough strains to which BmLBP binds were removed from the plasma within 30 min post-injection, whereas it required 8h for the clearance of smooth strains to which BmLBP does not bind. Observation of the hemocoel after the injection of Escherichia coli rough strain showed that melanized nodules were formed at 30 min post-injection when the clearance of injected E. coli cells had occurred. Fluorescence microscope observation revealed that E. coli cells were actually trapped in the nodules formed in vivo. Furthermore, plasma pre-treated E. coli rough cells (BmLBP bound) added to hemocytes isolated in vitro caused vigorous hemocyte aggregations with the bacteria, while plasma pre-treated smooth cells did not. The formation of aggregates was inhibited by anti-BmLBP serum pre-treatment, suggesting that BmLBP causes the clearance of bacteria by promoting hemocyte nodule formation.     

Role of chloroplast trienoic fatty acids in plant disease defense responses

Trienoic fatty acids (TAs) are the major polyunsaturated fatty acid species in the membrane lipids in plant cells. TAs are crucial for the adaptation to abiotic stresses, especially low- or high-temperature stress. We show that TAs in chloroplast membrane lipids are involved in defense responses against avirulent bacterial pathogens. Avirulent pathogen invasion of plants induces a transient production of reactive oxygen intermediates (ROI), programmed cell death and subsequent disease resistance. The Arabidopsis fad7fad8 mutation, which prevents the synthesis of TAs in chloroplast lipids, caused the reduction in ROI accumulation in leaves inoculated with Pseudomonas syringae pv. tomato DC3000 (avrRpm1). Linolenic acid, the most abundant TA, activated the NADPH oxidase that is responsible for ROI generation. TAs were transferred from chloroplast lipids to extrachloroplast lipids coincident with ROI accumulation after inoculation with Pst DC3000 (avrRpm1). Furthermore, the fad7fad8 mutant exhibited reduced cell death and was compromised in its resistance to several avirulent P. syringae strains. These results suggest that TAs derived from chloroplast lipids play an important role in the regulation of plant defense responses.     

Lactoferrin: Role in iron homeostasis and host defense against microbial infection

The transferrin family of non-heme iron binding glycoproteins are believed to play a central role in iron metabolism and have been implicated in iron transport, cellular iron delivery and control of the level of free iron in external secretions. Lactoferrin (LF) is a member of this family that is widely localized in external fluids including milk and mucosal secretions, in addition to being a prominent component of the secondary granules of neutrophils. Although structurally related to transferrin, LF appears to have a broader functional role mediated by both iron dependent and iron independent mechanisms. In this review, we will focus on our current understanding on the role of LF in regulating iron homeostasis and its role in host protection against microbial infection at the mucosal surface. In addition, recent insights obtained from analyzing the phenotypic consequences of LF ablation in lactoferrin knockout mice (LFKO), which challenge the long held dogma that LF is required for intestinal iron absorption in the neonate, are summarized.     

Ecochemical studies of interrelationships between epiphytic bacteria and host plants via secondary metabolites

The plant surface, which is representative of the phylloplane and rhizoplane, is a characteristic habitat for microorganisms. In this review, the ecological roles of phytoepiphytic bacteria will be described. The phylloplane and rhizoplane, which are adjacent to the atmosphere and soil sphere respectively, accumulate topically and/or selectively release secondary metabolites that are specific to the plant genera and species which reside within these regions. Some epiphytes have abilities to decarboxylate xenobiotic phenolic acids that have accumulated in the plant tissues and surfaces as a majority of such secondary metabolites. In physicochemically stressed soil, rhizosphere microflora often remedy such microenvironments within the rhizosphere in order to assist in the survival of the host, and some of the microfloral compositions behave as if they were symbionts. Specifically, some Sphingomonas spp., which are frequently isolated from the rhizosphere of acidic soil-tolerant plants in tropical zones, make possible the development of a rhizo-biocomplex. In this review, the possibility of rhizosphere regulation utilizing such a rhizo-biocomplex is discussed.