Gene expression signatures and small-molecule compounds link a protein kinase to Plasmodium falciparum motility

Calcium-dependent protein kinases play a crucial role in intracellular calcium signaling in plants, some algae and protozoa. In Plasmodium falciparum, calcium-dependent protein kinase 1 (PfCDPK1) is expressed during schizogony in the erythrocytic stage as well as in the sporozoite stage. It is coexpressed with genes that encode the parasite motor complex, a cellular component required for parasite invasion of host cells, parasite motility and potentially cytokinesis. A targeted gene-disruption approach demonstrated that pfcdpk1 seems to be essential for parasite viability. An in vitro biochemical screen using recombinant PfCDPK1 against a library of 20,000 compounds resulted in the identification of a series of structurally related 2,6,9-trisubstituted purines. Compound treatment caused sudden developmental arrest at the late schizont stage in P. falciparum and a large reduction in intracellular parasites in Toxoplasma gondii, which suggests a possible role for PfCDPK1 in regulation of parasite motility during egress and invasion.     

Pdr5-mediated multidrug resistance requires the CPY-vacuolar sorting protein Vps3: are xenobiotic compounds routed from the vacuole to plasma membrane transporters for efflux?

In Saccharomyces cerevisiae several members of the ATP-binding cassette transporter superfamily efflux a broad range of xenobiotic substrates from cells. The vacuole also plays a critical role in multidrug resistance. Mutations in genes such as VPS3 that are essential for vacuolar acidification and carboxypeptidase Y vacuolar protein-sorting are multidrug sensitive. A similar phenotype is also observed with deletions of VPS15, VPS34, and VPS38, which encode essential members of the carboxypeptidase Y vacuolar protein-sorting pathway. Prior to the work described herein, detoxification by transporters and the vacuole were presumed to function independently. We demonstrate that this is not the case. Significantly, Vps3 has an epistatic relationship with Pdr5, a major yeast multidrug transporter. Thus, a double pdr5, vps3 deletion mutant is no more multidrug sensitive than its isogenic single-mutant counterparts. Subcellular fractionation experiments and analysis of purified plasma membrane vesicles indicate, however, that a vps3 mutation does not affect the membrane-localization or ATPase activity of Pdr5 even though rhodamine 6G efflux is reduced significantly. This suggests that Vps3 and probably other members of the carboxypeptidase Y vacuolar protein-sorting pathway are required for relaying xenobiotic compounds to transporters in the membrane.     

Idiosyncratic responses to climate‐driven forest fragmentation and marine incursions in reed frogs from Central Africa and the Gulf of Guinea Islands

Organismal traits interact with environmental variation to mediate how species respond to shared landscapes. Thus, differences in traits related to dispersal ability or physiological tolerance may result in phylogeographic discordance among co‐distributed taxa, even when they are responding to common barriers. We quantified climatic suitability and stability, and phylogeographic divergence within three reed frog species complexes across the Guineo‐Congolian forests and Gulf of Guinea archipelago of Central Africa to investigate how they responded to a shared climatic and geological history. Our species‐specific estimates of climatic suitability through time are consistent with temporal and spatial heterogeneity in diversification among the species complexes, indicating that differences in ecological breadth may partly explain these idiosyncratic patterns. Likewise, we demonstrated that fluctuating sea levels periodically exposed a land bridge connecting Bioko Island with the mainland Guineo‐Congolian forest and that habitats across the exposed land bridge likely enabled dispersal in some species, but not in others. We did not find evidence that rivers are biogeographic barriers across any of the species complexes. Despite marked differences in the geographic extent of stable climates and temporal estimates of divergence among the species complexes, we recovered a shared pattern of intermittent climatic suitability with recent population connectivity and demographic expansion across the Congo Basin. This pattern supports the hypothesis that genetic exchange across the Congo Basin during humid periods, followed by vicariance during arid periods, has shaped regional diversity. Finally, we identified many distinct lineages among our focal taxa, some of which may reflect incipient or unrecognized species.     

Genetic loci associated with field resistance to late blight in offspring of Solanum phureja and S.tuberosum grown under short-day conditions

Field resistance to late blight – a fungal disease caused by Phytophthora infestans – has been genetically characterized by analyzing trait-marker association in a Solanum phureja (phu)×dihaploid Solanum tuberosum (dih-tbr) population. Trait data were developed at three locations over a 3-year period under natural infection pressure. RAPD (random amplified polymorphic DNA) and AFLP (amplified fragment length polymorphism)markers were used to develop anonymous genetic linkage groups subsequently anchored to potato chromosomes using mapped RFLP (restriction fragment length polymorphism), SSR (single sequence repeats) and AFLP markers. RFLP and SSR markers achieved the most-accurate anchoring. Two genetic maps were obtained, with 987.4 cM for phu and 773.7 cM for dih-tbr. Trait-marker association was revealed by single-marker and interval mapping analyses. Two important QTLs (quantitative trait loci) were detected on chromosomes VII and XII as a contribution from both parents, totalling up to 16% and 43%, respectively, of the phenotypic variation (PH). One additional QTL was detected on chromosome XI (up to 11% of the PH) as a contribution from the phu parent, and three others were detected on chromosome III (up to 13% of the PH), chromosome V (up to 11% of the PH) and chromosome VIII (up to 11% of the PH) as a contribution from the dih-tbr parent. Our results reveal new genetic loci of the potato genome that contribute to resistance to late blight. We postulate that some of these loci could be related to plant growth under short-day conditions. Received: 5 July 2000 / Accepted: 17 November 2000     

Competitive interactions between forest trees are driven by species' trait hierarchy, not phylogenetic or functional similarity: implications for forest community assembly

The relative importance of competition vs. environmental filtering in the assembly of communities is commonly inferred from their functional and phylogenetic structure, on the grounds that similar species compete most strongly for resources and are therefore less likely to coexist locally. This approach ignores the possibility that competitive effects can be determined by relative positions of species on a hierarchy of competitive ability. Using growth data, we estimated 275 interaction coefficients between tree species in the French mountains. We show that interaction strengths are mainly driven by trait hierarchy and not by functional or phylogenetic similarity. On the basis of this result, we thus propose that functional and phylogenetic convergence in local tree community might be due to competition-sorting species with different competitive abilities and not only environmental filtering as commonly assumed. We then show a functional and phylogenetic convergence of forest structure with increasing plot age, which supports this view.     

Two Feedback-Insensitive Enzymes of the Aspartate Pathway in Nicotiana sylvestris

Lysine and threonine overproducer mutants in Nicotiana sylvestris, characterized by an altered regulation of, respectively, dihydrodipicolinate synthase and aspartate kinase activities, were crossed to assess the effects of the simultaneous presence of these genes on the biosynthesis of aspartate-derived amino acids. The monogenic dominant behavior of both resistance traits was confirmed, and their loci were found to be unlinked. Study of the inhibition properties of dihydrodipicolinate synthase and aspartate kinase activities in RAEC-1 × RLT 70 confirmed the heterozygote state of both mutations, because only half of their lysine-sensitive activity could still be inhibited by this negative effector. Analysis of the free amino acid pool during the growth of the double mutant revealed a major free lysine overproduction reaching up to 50% of the total pool, whereas the other aspartate-derived amino acids remained equally or even less abundant than in the wild type. An abnormal phenotype was clearly associated with such high levels of lysine accumulation, which points out the possible role of this amino acid in the developmental features of the plant. Comparison of the amino acid content, free and total (free + protein-bound), between the wild type, the two mutants, and the double mutant obtained by crossing them brings new insights on the regulation of the aspartate pathway, and on its implications in relationship to plant nutritional value improvement.