Proanthocyanidin biosynthesis--still more questions than answers?

Proanthocyanidins, also known as condensed tannins, are oligomers or polymers of flavan-3-ol units. In spite of important breakthroughs in our understanding of the biosynthesis of the major building blocks of proanthocyanidins, (+)-catechin and (-)-epicatechin, important questions still remain to be answered as to the exact nature of the molecular species that undergo polymerization, and the mechanisms of assembly. We review the structures of proanthocyanidins reported over the past 12 years in the context of biosynthesis, and summarize the outstanding questions concerning synthesis of proanthocyanidins from the chemical, biochemical and molecular genetic perspectives.     

More plastids in human parasites?

Trypanosomatid parasites are disease agents with an extraordinarily broad host range including humans, livestock and plants. Recent work has revealed that trypanosomatids harbour numerous genes sharing apparent common ancestry with plants and/or bacteria. Although there is no evidence of a plastid (chloroplast-like organelle) in trypanosomatids, the presence of such genes suggests lateral gene transfer from some photosynthetic organism(s) during trypanosomatid evolution. Remarkably, many products of these horizontally acquired genes now function in the glycosome, a highly modified peroxisome unique to trypanosomatids and their near relatives.     

P-bodies and mitochondria: Which place in RNA interference?

Micro-RNAs (miRNAs) are major actors of RNA interference (RNAi), a regulation pathway which leads to translational repression and/or degradation of specific mRNAs. They provide target specificity by incorporating into the RISC complex and guiding its binding to mRNA. Since the discovery of RNAi, many progresses have been made on the mechanism of action of the RISC complex and on the identification of target mRNAs. However, the regulation of RNAi has been poorly investigated so far. Recently, various studies have revealed physical and functional relationships between RNAi, P-bodies and mitochondria. This review intends to recapitulate these data and discuss their potential importance in cell metabolism.     

DNA evidence: Wrong answers or wrong questions?

Much of the controversy over DNA evidence is due to the way in which forensic scientific evidence has classically been presented. The orthodox approach is to consider whether two samples match according to a predetermined criterion. If they do, the fact of match is reported along with an estimate of the frequency of the characteristics. This method fails to address the questions raised in court cases, diverts argument into irrelevancies and stultifies research. Presentation of evidence in the form of likelihood ratios, on the other hand, forces the witness to answer the questions the court is interested in and makes apparent lines of research required to increase our understanding.Editor's commentsThe authors reiterate the crucial role of likelihood ratios in presenting forensic evidence, and so continue the crusade mounted by Evett, Buckleton and others.     

Pushing for answers: is myosin V directly involved in moving mitochondria?

In budding yeast, the actin-based class V myosin motors, Myo2 and Myo4, transport virtually all organelles from mother to bud during cell division. Until recently, it appeared that mitochondria may be an exception, with studies showing that the Arp2/3 complex is required for their movement. However, several recent studies have proposed that Myo2 has a direct involvement in mitochondria inheritance. In this issue, Altmann et al. (Altmann, K., M. Frank, D. Neumann, S. Jakobs, and B. Westermann. 2008. J. Cell Biol. 181:119-130) provide the strongest support yet that Myo2 and its associated light chain Mlc1 function directly and significantly in both mitochondria-actin interactions and in the movement of mitochondria from mother to bud. The conflicting functions of Arp 2/3 and Myo2 may be reconciled by the existence of multiple pathways involved in mitochondrial transport.     

Antifungal proteins: More than antimicrobials?

Antimicrobial proteins (AMPs) are widely distributed in nature. In higher eukaryotes, AMPs provide the host with an important defence mechanism against invading pathogens. AMPs of lower eukaryotes and prokaryotes may support successful competition for nutrients with other microorganisms of the same ecological niche. AMPs show a vast variety in structure, function, antimicrobial spectrum and mechanism of action. Most interestingly, there is growing evidence that AMPs also fulfil important biological functions other than antimicrobial activity. The present review focuses on the mechanistic function of small, cationic, cysteine-rich AMPs of mammals, insects, plants and fungi with antifungal activity and specifically aims at summarizing current knowledge concerning additional biological properties which opens novel aspects for their future use in medicine, agriculture and biotechnology.     

Antifungal proteins: More than antimicrobials?

Antimicrobial proteins (AMPs) are widely distributed in nature. In higher eukaryotes, AMPs provide the host with an important defence mechanism against invading pathogens. AMPs of lower eukaryotes and prokaryotes may support successful competition for nutrients with other microorganisms of the same ecological niche. AMPs show a vast variety in structure, function, antimicrobial spectrum and mechanism of action. Most interestingly, there is growing evidence that AMPs also fulfil important biological functions other than antimicrobial activity. The present review focuses on the mechanistic function of small, cationic, cysteine-rich AMPs of mammals, insects, plants and fungi with antifungal activity and specifically aims at summarizing current knowledge concerning additional biological properties which opens novel aspects for their future use in medicine, agriculture and biotechnology.     

Plant-endophyte-herbivore interactions: More than just alkaloids?

A recent paper by Rasmussen et al., (New Phytol 2007; 173:787–97) describes the interactions between Lolium perenne cultivars with contrasting carbohydrate content and the symbiotic fungal endophyte Neotyphodium lolii at different levels of nitrogen supply. In a subsequent study undertaken by Rasmussen et al., (Plant Physiol 2008; 146:1440–53) 66 metabolic variables were analysed in the same material, revealing widespread effects of endophyte infection, N supply and cultivar carbohydrate content on both primary and secondary metabolites. Here, we link insect numerical responses to these metabolic responses using multiple regression analysis.Key words: Neotyphodium lolii, Lolium perenne, high sugar grasses, metabolomics, insect herbivoresPasture grasses are often infected with symbiotic fungal endophytes and benefits for host plants arising out of these associations are generally ascribed to endophyte produced anti-herbivorous alkaloids. We tested the effects of (i) infection with three strains of endophytes differing in their alkaloid profiles, (ii) high vs. low nitrogen (N) supply, and (iii) ryegrass cultivars with high vs. control levels of water soluble carbohydrates (WSCs) on numerical insect responses (aphids, thrips, mites). A difference in WSC content between the cultivars had no significant effect on insect numbers, whereas high N compared to low N supply increased mites, thrips and alate Rhopalosiphum spp., but decreased apterous Rhopalosiphum spp. The effect of endophyte infection was strain dependant and differed for the different insects.A total of 66 metabolic variables of the same plants analysed prior to insect treatment were linked to insect responses using multiple regression analysis. One of the major conclusions to be drawn is that alkaloids are not always the most important factor influencing numerical insect responses which will also be determined by other metabolites, clearly indicating the importance of metabolomics type studies to point the way toward a mechanistic explanation of grass-endophyte-herbivore interactions.Grass species are often hosts of symbiotic clavicipitaceous endophytic fungi¹ residing in the apoplastic spaces of above ground plant parts and usually not causing any visible symptoms of infection.^2–4 These fungal symbionts confer protection from insect herbivory to their host plants through alkaloids,^5–8 some of which (ergovaline, lolitrem B) are also toxic to grazing mammals.^9,10 Natural endophyte strains lacking these mammalian toxins, but still retaining at least some of their insect deterring features, have been commercialized and are now widely used in ryegrass and tall fescue based pastures.^11,12     

Butyrolactone: More than a Kinase Inhibitor?

No Abstract Available

Key Words:

Butryolactone, Kinase inhibitor, cyclin-dependent kinase inhibitor, p21, p53     

How clonal are human mitochondria?

Phylogenetic trees constructed using human mitochondrial sequences contain a large number of homoplasies. These are due either to repeated mutation or to recombination between mitochondrial lineages. We show that a tree constructed using synonymous variation in the protein coding sequences of 29 largely complete human mitochondrial molecules contains 22 homoplasies at 32 phylogenetically informative sites. This level of homoplasy is very unlikely if inheritance is clonal, even if we take into account base composition bias. There must either be 'hypervariable' sites or recombination between mitochondria. We present evidence which suggests that hypervariable sites do not exist in our data. It therefore seems likely that recombination has occurred between mitochondrial lineages in humans.     

Is Working More Costly than Waiting in Monkeys?

We studied how value for instrumental action is discounted by predicted effort and delay. The monkeys were trained to perform instrumental trials that required a bar release when a visual target changed from red-to-green. There were two trial conditions. In delay trials, after the monkeys performed one instrumental trial correctly a reward was delivered 0–7 seconds later. In work trials, the monkeys had to perform 0, 1, or 2 additional instrumental trials to obtain a reward. The lengths of trials in delay matched the time it took to complete work trials. The length of delay or number of trials was indicated by a visual cue presented throughout the trial. Our hypothesis was that the monkeys would all show temporal discounting of reward in the delay trials, and that in the work trials the monkeys’ performance might reflect an additional cost due to working. The error rate increased linearly as remaining cost increased for all 8 monkeys. For 4 monkeys the error rate was significantly larger in work trials than in delay trials (effort sensitive monkeys). For the other 4 monkeys there was no significant difference in error rate (effort insensitive monkeys). Since the error rate has an inverse relation with value for action, these results suggest that value is discounted hyperbolically by effort as well as by delay. Error rates generally increased as the testing sessions progressed and the total reward accumulated (i.e., effect of reward devaluation). The relative impact of delay and effort on error rates was reasonably stable within subjects. Thus, within the monkey population there seems to be a significant dichotomy in the sensitivity governing whether working is more costly than waiting, possibly arising from a constitutional or genetic trait.     

Is there VDAC in cell compartments other than the mitochondria?

Higher eukaryotes, including mammals and plants, express a family of VDAC proteins each encoded by a distinct gene. Two human genes encoding VDAC isoforms (HVDAC1 and HVDAC2) have been characterized in greatest detail. These genes generate three proteins that differ primarily by the addition of distinct N terminal extensions in HVDAC2 and HVDAC2, a splice variant of HVDAC2, relative to HVDAC1. Since N terminal sequences have been demonstrated to target many proteins to appropriate subcellular compartments, this observation raises the possibility that the N terminal differences found in HVDAC isoforms may lead to targeting of each protein to different cellular locations. Consistent with this hypothesis, a large number of reports have provided evidence consistent with the notion that HVDAC1 and its homolog in related mammalian species may specifically be present in the plasma membrane or other nonmitochondrial cellular compartments. Here, we review this information and conclude that if VDAC molecules are present at nonmitochondrial locations in mammalian cells, these are unlikely to be the known products of the HVDAC1 or HVDAC2 genes.     

Centriole duplication: centrin in on answers?

Many aspects of centriole biology remain mysterious. A new study has shed light on the role of the centriolar protein centrin-2: reducing levels of centrin-2 in HeLa cells has been found to block centriole duplication, eventually leading to cell death.     

Histone acetyltransferase 1: More than just an enzyme?

Histone acetyltransferase 1 (HAT1) is an enzyme that is likely to be responsible for the acetylation that occurs on lysines 5 and 12 of the NH(2)-terminal tail of newly synthesized histone H4. Initial studies suggested that, despite its evolutionary conservation, this modification of new histone H4 played only a minor role in chromatin assembly. However, a number of recent studies have brought into focus the important role of both this modification and HAT1 in histone dynamics. Surprisingly, the function of HAT1 in chromatin assembly may extend beyond just its catalytic activity to include its role as a major histone binding protein. These results are incorporated into a model for the function of HAT1 in histone deposition and chromatin assembly. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.