Implications of toxins in the ecology and evolution of plant pathogenic microorganisms: Bacteria

This review attempts to rationalise what is known about bacterial phytotoxins and associate it with the ecology and possible evolution of the producing organisms. Study of non-toxin producing variants gives insight into the ecological role of the toxin. Elucidation of chemical structures of phytotoxins has shown that many exist as families of analogous compounds. Studies on the variation of chemical structures and how they are distributed across species and genera can lead to development of hypotheses on evolutionary relationships. Knowledge on biosynthetic pathways to tosins allows recognition of specific enzymatic steps involved in developing the characteristic features of the structures. Phytotoxins often have a potent biochemical activity, and in some cases the producing organism has associated mechanisms to prevent action of the toxin upon itself; in such cases toxigenesis is clearly not a chance event. The various aspects of bacterial toxigenesis indicate that bacterial phytotoxins are special secondary metabolic products that play beneficial roles to the producing organisms in their various ecological niches.     

Increased formation of arginine deiminase byClostridium perfringens FD-1 growing in the presence of caffeine

Summary Caffeine slowed growth and markedly increased the formation of arginine deiminase in growingC. perfringens FD-1 when dextrin, but not maltose or maltotriose, served as the energy source. It is postulated that the ability of caffeine to induce arginine deiminase is related to an inhibition of polysaccharide utilization, resulting in a shift-down condition known to induce arginine deiminase and other enzymes in bacteria.     

Ornithine decarboxylase,S-adenosyl-L-methionine decarboxylase and arginine decarboxylase fromMycobacterium bovis (BCG)

Summary Ornithine decarboxylase (ODC), S-adenosyl-L-methionine decarboxylase (AMDC) and arginine decarboxylase (ADC) activities were detected for the first time in extracts ofMycobacterium bovis (BCG). All the decarboxylases differed from corresponding known bacterial decarboxylases in that: a) ODC did not require GTP for activity; b) ODC was not inhibited by any known inhibitor of bacterial ODCs; c) AMDC and ADC did not require Mg²⁺-ion for activity and were not markedly inhibited by any known inhibitor of the decarboxylases of other bacteria.     

The complexity of mitogen-activated protein kinases (MAPKs) made simple

The mitogen-activated protein kinase (MAPK) pathways are known to be involved in various processes of growth, differentiation and cell death. In spite of their ubiquitous presence and seemingly enormous cross-talk with each other, their action is very specific. This review deals with various aspects of the three different MAPK pathways (ERK, p38 and JNK) and how their specificity is brought about. Received 1 April 2008; received after revision 18 June 2008; accepted 18 June 2008     

Unique sex chromosome mediated behavioral response specificity of hybrid male European corn borer moths

Unlike the narrow response windows exhibited by the parent races, hybrid male European corn borers resulting from crosses of the E and Z races respond to a wide range of sex pheromone blends. The F₁ response profile consists of some individuals that respond to both the Z pheromone and the 6535 E/Z blend produced by F₁ females. Some F₁ males fail to respond to any blend and some do not respond as broadly as others. The hybrid male populations, however, are not tuned optimally to the pheromone blend produced by F₁ females and there is no coupling of F₁ blend production and response.     

Conservation,evolution, and specificity in cellular control by protein phosphorylation

The glycolytic control enzyme phosphofructokinase from the parasitic nematodeAscaris lumbricodies is regulated by reversible phosphorylation. The enzyme is phosphorylated by an atypical cyclic adenosine monophosphate (cAMP)-dependent protein kinase whose substrate specificity deviates from that of the mammalian protein kinase. This variation is explained by structural peculiarities on the surface part of the catalytic groove of the protein kinase. Also, the protein phosphatases responsible for the reversal of phosphorylation appear to act specifically in glycolysis and are different from those participating in regulation of glycogenolysis.     

Seasonality in the reproductive phenology ofFicus: Its evolution and consequences

Summary Ficus can only reproduce if they are pollinated by mutualistic wasps that breed within the figs. Pollen-loaded wasps enter the figs when the female flowers are receptive. Several weeks later, their offspring load pollen within the fig and then emerge. As individual trees typically produce crops of synchronous figs at long intervals, the shortlived wasps have to move to another, receptive, tree. The wasp population can only survive, and hence the fig population reproduce, if there are trees fruiting all over the year. When only few trees are present within a population gaps in the flowering sequence may lead to the extinction of the local pollinator population. Two models are presented. One investigates the number of trees necessary in order to sustain a local pollinator population when the tree population has a seasonal pattern of fruiting. The second model investigates how such a seasonal pattern may evolve within a fig population as a result of individual selection on the trees. It is shown that pollinator populations are fragilized under seasonal conditions. Hence, the breeding system ofFicus limits their expansion into highly seasonal habitats. Seasonal habitats may also lead to seasonal adjustment of male versus female investments and to the evolution of dioecy.     

Role of toxins in evolution and ecology of plant pathogenic fungi

Many fungal pathogens of plants adapt readily to changes in agriculture. Among the most revealing is a fungal group whose species produce host-selective toxins as key determinants of disease. Several lines of evidence support the hypothesis that these fungi evolved from opportunistic, low-grade pathogens by gaining new genetic information leading to toxin production; in some species, toxin production is known to be under single gene control. as a result of this evolution, these fungi became virulent and host-specialized. The best-known model cases belong to the generaCochliobolus andAlternaria; there are suggestions of evolutionary lines among these genera, with species that range from saprophytes to opportunists to specialized pathogens. Host specialization can lead to genetic isolation, a first step in speciation. Ability to produce host-selective toxin has allowed these fungi to exploit the monocultures and genetic uniformity of modern agriculture. Destructive epidemics have been the result.     

What’s new in the renin-angiotensin system?

Angiotensin-converting enzyme (ACE) is a zinc- and chloride-dependent metallopeptidase that plays a vital role in the metabolism of biologically active peptides. Until recently, much of the inhibitor design and mechanism of action of this ubiquitous enzyme was based on the structures of carboxypeptidase A and thermolysin. When compared to the recently solved structures of the testis isoform of ACE (tACE) and its Drosophila homologue (AnCE), carboxypeptidase A showed little structural homology outside of the active site, while thermolysin revealed significant but less marked overall similarity. The ellipsoid-shaped structure of tACE, which has a preponderance of -helices, is characterised by a core channel that has a constriction approximately 10 Å from its opening where the zinc-binding active site is located. Comparison of the native protein with the inhibitor-bound form (lisinopril-tACE) does not reveal any striking differences in the conformation of the inhibitor binding site, disfavouring an open and closed configuration. However, the inhibitor complex does provide insights into the network of hydrogen-bonding and ionic interactions in the active site as well as the mechanism of ACE substrate hydrolysis. The three-dimensional structure of ACE now paves the way for the rational design of a new generation of domain-selective ACE inhibitors.     

Recent observations on the structure and the properties of yeast NMN adenylyltransferase

Summary A homogeneous preparation of yeast NMN adenylyltransferase (EC 2.7.7.1) showed microheterogeneity, which was revealed by FPLC (Fast Protein Liquid Chromatography) ion exchange chromatography. The resolved components have been characterized with respect to electrophoretic behavior and adenine content. The results led to a hypothesis about a possible role of poly(ADP-ribosylation) in modulating the enzyme activity.     

Inhibition of invasion and intraerythrocytic development ofPlasmodium falciparum by kinase inhibitors

We have examined the effects of seven protein kinase inhibitors (staurosporine, genistein, methyl 2,5-dihydroxycinnamate, tyrphostins B44 and B46, lavendustin A and R03) on the erythrocytic cycle of the malaria parasite,Plasmodium falciparum. One (staurosporine) strongly inhibits serine/threonine kinases, but the remainder all exhibit a strong preference for tyrosine kinases. We have been able to discriminate between effects on invasion and on intraerythrocytic development. All reagents impeded development of intraerythrocytic parasites, though at widely differing concentrations, from the sub-micromolar to the millimolar. Several inhibitors, including staurosporine, also reduced invasion. The phosphatase inhibitor, okadaic acid, had a strong inhibitory effect both on invasion and development. The regulation of malaria development by phosphorylation or dephosphorylation reactions at several points in the blood-stage cycle is implied.     

Photoregulation of some enzymes fromNeurospora crassa

Summary Light-grown cultures ofNeurospora crassa showed photoregulation of a number of enzymes. Proteases and cytosolic malate dehydrogenase showed an increase in activity. There was a decrease in the activity of mitochondrial malate dehydrogenase, isocitrate dehydrogenase and cytosolic glucose-6P-dehydrogenase, isocitrate dehydrogenase and isocitrate lyase.     

Concordant change in mitochondrial and nuclear genes in a hybrid zone between two frog species (genusBombina)

Summary In contrast to results in other studies, nuclear and mitochondrial genes were found to change concordantly in a transect across the hybrid zone betweenBombina bombina andBombina variegata. mtDNAs of both species are found in populations in the central part of the zone, whereas populations at its margins contain mtDNA corresponding to nuclear genomes.     

RNA editing in plant organelles: machinery, physiological function and evolution

In plants, RNA editing is a process for converting a specific nucleotide of RNA from C to U and less frequently from U to C in mitochondria and plastids. To specify the site of editing, the cis-element adjacent to the editing site functions as a binding site for the trans-acting factor. Genetic approaches using Arabidopsis thaliana have clarified that a member of the protein family with pentatricopeptide repeat (PPR) motifs is essential for RNA editing to generate a translational initiation codon of the chloroplast ndhD gene. The PPR motif is a highly degenerate unit of 35 amino acids and appears as tandem repeats in proteins that are involved in RNA maturation steps in mitochondria and plastids. The Arabidopsis genome encodes approximately 450 members of the PPR family, some of which possibly function as trans-acting factors binding the cis-elements of the RNA editing sites to facilitate access of an unidentified RNA editing enzyme. Based on this breakthrough in the research on plant RNA editing, I would like to discuss the possible steps of co-evolution of RNA editing events and PPR proteins. Received 30 September 2005; received after revision 5 November 2005; accepted 28 November 2005     

Dominance for enzyme activity inDrosophila melanogaster

Summary A regulatory element tightly linked to theGpdh locus inDrosophila melanogaster has been isolated from a natural population. Flies homozygous for second chromosomes bearing the element,H31, have half the GPDH activity of normal homozygotes. Heterozygotes betweenH31 andF orS alleles exhibit dominance in GPDH activity. Heterozygotes betweenH31, F orS andDf(2L) GdhA have half the diploid level. The contribution of theS allele to the activity inS/H31 heterozygotes is more than four times that ofH31. The regulatory element distinguishingH31 is tightly linked to theGpdh ⁺ locus.     

Endocytosis and inositol hexakisphosphate levels inras transformants ofDictyostelium discoideum amoebae

Summary Fluid-phase pinocytosis kinetics and lysosomal enzyme secretion parameters were measured inDictyostelium discoideum amoebae constructed from strain AX3 by transformation with a multicopy plasmid carrying either a normalras gene (ras-Gly12), a mutatedras gene (ras-Thr12) or by the vector carrying the geneticin resistance gene only (pDNEO2). It was found that the pinocytosis rate and extent as well as the lysosomal enzyme secretion were slightly different in the three strains. These changes, however, were related to minor modifications of the cellular volumes. The overall concentration of inositol hexakisphosphate was similar in the three strains.This work was supported in part by a grant from the Ligue Nationale Française contre le Cancer (n^o 880258) to MS, and by a grant from the Fonds National Suisse de la Recherche Scientifique (No. 3.623-087) to CR.     

Duplications of additively acting genes in the evolution of a plant (Microseris pygmaea)

Summary Crosses betweenMicroseris pygmaea (10 pappus parts per fruit) andM. bigelovii (5 pappus parts) have revealed 10-determining genes that additively determine the average number of pappus parts in the hybrids. One or two such genes are found in different populations. Two independent duplications of the original 10-determining gene seem to have occurred.     

Serological and genetical studies on the evolution of substrate specificity of flavone glycosyltransferase genes inSilene

Summary The variation in flavone glycosylation patterns inSilene is the result of the expression of six genetic loci, which control either the presence of allozymes differing in substrate specificity or isozymes regulated differently during development. Serological studies showed that at least three of these six loci are evolutionarily related. The genetic mechanisms leading to these complicated variation patterns and the role of this polymorphism for the plant in its interaction with the environment are discussed.     

Studies on the fungal phytotoxin victorin: Structures of three novel amino acids from the acid hydrolyzate

Summary The host-selective phytotoxin victorin, produced by the fungusCochliobolus victoriae, was found to be at least partially peptidic in nature, and did not contain victoxinine. The exact mass of the M-H ion was measured by FABMS as 795.1877. Derivatives of three major acid hydrolysis products were isolated. The structures of the corresponding amino acids were assigned as 2S,3R-3-hydroxyleucine, 5,5-dichloroleucine, and 3-hydroxylysine. A into victorin by the fungus in vivo.