Differentially expressed genes and proteins upon drought acclimation in tolerant and sensitive genotypes of Coffea canephora

The aim of this study was to investigate the molecular mechanisms underlying drought acclimation in coffee plants by the identification of candidate genes (CGs) using different approaches. The first approach used the data generated during the Brazilian Coffee expressed sequence tag (EST) project to select 13 CGs by an in silico analysis (electronic northern). The second approach was based on screening macroarrays spotted with plasmid DNA (coffee ESTs) with separate hybridizations using leaf cDNA probes from drought-tolerant and susceptible clones of Coffea canephora var. Conilon, grown under different water regimes. This allowed the isolation of seven additional CGs. The third approach used two-dimensional gel electrophoresis to identify proteins displaying differential accumulation in leaves of drought-tolerant and susceptible clones of C. canephora. Six of them were characterized by MALDI-TOF-MS/MS (matrix-assisted laser desorption-time of flight-tandem mass spectrometry) and the corresponding proteins were identified. Finally, additional CGs were selected from the literature, and quantitative real-time polymerase chain reaction (qPCR) was performed to analyse the expression of all identified CGs. Altogether, >40 genes presenting differential gene expression during drought acclimation were identified, some of them showing different expression profiles between drought-tolerant and susceptible clones. Based on the obtained results, it can be concluded that factors involved a complex network of responses probably involving the abscisic signalling pathway and nitric oxide are major molecular determinants that might explain the better efficiency in controlling stomata closure and transpiration displayed by drought-tolerant clones of C. canephora.     

ERGOSTEROL BIOSYNTHESIS: A FUNGAL PATHWAY FOR LIFE ON LAND?

Sterols, essential lipids of most eukaryotic cells, ensure important structural and signaling functions. The selection pressure that has led to different dominant sterols in the three eukaryotic kingdoms remains unknown. Here, we investigated the influence of the progression in the different steps of the ergosterol biosynthetic pathway (EBP) on the yeast resistance to transitions from aqueous to aerial media, typical perturbations of the higher fungi habitats. Five mutants of the EBP (ergΔ), accumulating different sterol intermediates in the EBP, and the wild‐type (WT) strain were exposed to drying under atmospheric air or nitrogen and wetting. Results show that the progression in the EBP parallels an increase in the yeast resistance to air‐drying with a maximal survival rate for the WT strain. When drying/wetting was performed under nitrogen, yeast survival was higher, particularly for the earlier mutants of the EBP. Thus, ergosterol, through its protective role against mechanical and oxidative stress, might have been selected by the pressure induced by drying/wetting cycles occurring in the fungi habitats. These results support the Bloch hypothesis, which postulates that the properties of sterols are gradually optimized for function along the biosynthetic pathway and provide a response to the enduring question “why ergosterol in fungi?”.     

FOOD PLANT DERIVED DISEASE TOLERANCE AND RESISTANCE IN A NATURAL BUTTERFLY‐PLANT‐PARASITE INTERACTIONS

Organisms can protect themselves against parasite‐induced fitness costs through resistance or tolerance. Resistance includes mechanisms that prevent infection or limit parasite growth while tolerance alleviates the fitness costs from parasitism without limiting infection. Although tolerance and resistance affect host–parasite coevolution in fundamentally different ways, tolerance has often been ignored in animal–parasite systems. Where it has been studied, tolerance has been assumed to be a genetic mechanism, unaffected by the host environment. Here we studied the effects of host ecology on tolerance and resistance to infection by rearing monarch butterflies on 12 different species of milkweed food plants and infecting them with a naturally occurring protozoan parasite. Our results show that monarch butterflies experience different levels of tolerance to parasitism depending on the species of milkweed that they feed on, with some species providing over twofold greater tolerance than other milkweed species. Resistance was also affected by milkweed species, but there was no relationship between milkweed‐conferred resistance and tolerance. Chemical analysis suggests that infected monarchs obtain highest fitness when reared on milkweeds with an intermediate concentration, diversity, and polarity of toxic secondary plant chemicals known as cardenolides. Our results demonstrate that environmental factors—such as interacting species in ecological food webs—are important drivers of disease tolerance.     

Synthesis of novel 7-oxo and 7-hydroxy trifluoroallocolchicinoids with cytotoxic effect

The synthesis of 7-oxo and 7-hydroxy trifluoroallocolchicinoids was achieved through the intramolecular cyclization of o-phenyl-β-phenylalanines. The resulting compounds were evaluated for their cytotoxic activity against KB cells and their inhibitory effect towards the polymerization of tubulin. The results yielded some potent cytotoxic compounds with correlated partial antitubulin effect.     

Influence of the skeleton on the cytotoxicity of flavonoids

Analogs of 3'-amino-5-hydroxy-3,6,7,8,4'-pentamethoxy-flavone, a strongly cytotoxic and antimitotic semisynthetic flavone, were synthesized in the aurone, isoflavone and isoflavanone series. Comparison of the biological activity of these new compounds with the reference showed a potent cytotoxicity only in the flavone series. Influence of the hydroxy group (at C-5 in flavones, at C-4 in aurones) on the cytotoxicity, known to be favorable in flavones, was found to be detrimental in aurones. This observation was related to the hydrogen bonding formed with the carbonyl group, strong in the flavones, but of weak intensity in the aurones.     

Quantitative trait locus mapping of yield-related components and oligogenic control of the cap color of the button mushroom, Agaricus bisporus

As in other crops, yield is an important trait to be selected for in edible mushrooms, but its inheritance is poorly understood. Therefore, we have investigated the complex genetic architecture of yield-related traits in Agaricus bisporus through the mapping of quantitative trait loci (QTL), using second-generation hybrid progeny derived from a cross between a wild strain and a commercial cultivar. Yield, average weight per mushroom, number of fruiting bodies per m(2), earliness, and cap color were evaluated in two independent experiments. A total of 23 QTL were detected for 7 yield-related traits. These QTL together explained between 21% (two-flushes yield) and 59% (earliness) of the phenotypic variation. Fifteen QTL (65%) were consistent between the two experiments. Four regions underlying significant QTL controlling yield, average weight, and number were detected on linkage groups II, III, IV, and X, suggesting a pleiotropic effect or tight linkage. Up to six QTL were identified for earliness. The PPC1 locus, together with two additional genomic regions, explained up to 90% of the phenotypic variation of the cap color. Alleles from the wild parent showed beneficial effects for some yield traits, suggesting that the wild germ plasm is a valuable source of variation for several agronomic traits. Our results constitute a key step toward marker-assisted selection and provide a solid foundation to go further into the biological mechanisms controlling productive traits in the button mushroom.     

Long-term in situ dynamics of the fungal communities in a multi-contaminated soil are mainly driven by plants

The fungal communities of a multi-contaminated soil polluted by polycyclic aromatic hydrocarbons and heavy metals (NM) were studied within a long-term in situ experiment of natural attenuation assisted by plants. Three treatments were monitored: bare soil (NM-BS), soil planted with alfalfa and inoculated with mycorrhizal fungi (NM-Msm), and soil with spontaneous vegetation (NM-SV). The same soil after thermal desorption (TD) was planted with alfalfa and inoculated with mycorrhizal fungi (TD-Msm). Twice a year for 5?years, the fungal abundance and the community structure were evaluated by real-time PCR and temporal temperature gradient gel electrophoresis targeting 18S rRNA genes. The fungal abundance increased over time and was higher in planted than in bare NM soil and in TD than in NM soil. The Shannon diversity index (H') increased during the first 2?years with the emergence of more than 30 ribotypes, but decreased after 3?years with the selection of a few competitive species, mostly Ascomycetes. H' was higher under complex plant assemblage (NM-SV) than in the NM-BS plots but did not differ between NM and TD soils planted with alfalfa. These results indicated that even in a highly polluted soil, the plant cover was the main driver of the fungal community structure.     

Bacterial communities associated with healthy and Acropora white syndrome-affected corals from American Samoa

Acropora white syndrome (AWS) is characterized by rapid tissue loss revealing the white underlying skeleton and affects corals worldwide; however, reports of causal agents are conflicting. Samples were collected from healthy and diseased corals and seawater around American Samoa and bacteria associated with AWS characterized using both culture-dependent and culture-independent methods, from coral mucus and tissue slurries, respectively. Bacterial 16S rRNA gene clone libraries derived from coral tissue were dominated by the Gammaproteobacteria, and Jaccard's distances calculated between the clone libraries showed that those from diseased corals were more similar to each other than to those from healthy corals. 16S rRNA genes from 78 culturable coral mucus isolates also revealed a distinct partitioning of bacterial genera into healthy and diseased corals. Isolates identified as Vibrionaceae were further characterized by multilocus sequence typing, revealing that whilst several Vibrio spp. were found to be associated with AWS lesions, a recently described species, Vibrio owensii, was prevalent amongst cultured Vibrio isolates. Unaffected tissues from corals with AWS had a different microbiota than normal Acropora as found by others. Determining whether a microbial shift occurs prior to disease outbreaks will be a useful avenue of pursuit and could be helpful in detecting prodromal signs of coral disease prior to manifestation of lesions.     

The full-length Streptococcus pneumoniae major pilin RrgB crystallizes in a fibre-like structure, which presents the D1 isopeptide bond and provides details on the mechanism of pilus polymerization

RrgB is the major pilin which forms the pneumococcal pilus backbone. We report the high-resolution crystal structure of the full-length form of RrgB containing the IPQTG sorting motif. The RrgB fold is organized into four distinct domains, D1-D4, each of which is stabilized by an isopeptide bond. Crystal packing revealed a head-to-tail organization involving the interaction of the IPQTG motif into the D1 domain of two successive RrgB monomers. This fibrillar assembly, which fits into the electron microscopy density map of the native pilus, probably induces the formation of the D1 isopeptide bond as observed for the first time in the present study, since neither in published structures nor in soluble RrgB produced in Escherichia coli or in Streptococcus pneumoniae is the D1 bond present. Experiments performed in live bacteria confirmed that the intermolecular bond linking the RrgB subunits takes place between the IPQTG motif of one RrgB subunit and the Lys183 pilin motif residue of an adjacent RrgB subunit. In addition, we present data indicating that the D1 isopeptide bond is involved in RrgB stabilization. In conclusion, the crystal RrgB fibre is a compelling model for deciphering the molecular details required to generate the pneumococcal pilus.