Biochemical response between insects and plants: an investigation of enzyme activity in the digestive system of Leucoptera coffeella (Lepidoptera: Lyonetiidae) and leaves of Coffea arabica (Rubiaceae) after herbivory

Plant defence mechanisms can reduce the digestive enzyme activity of insect pests. The aim of this study was to determine the relationship between the production of proteinase inhibitors, lipoxygenase and polyphenol oxidase activity in Coffea arabica (Catuai IAC 15) plants, and the digestive enzyme activity in the pest Leucoptera coffeella (Lepidoptera: Lyonetiidae) after feeding on the plant. The production of proteinase inhibitors was evaluated with L‐BApNA as a substrate. We studied lipoxygenase activity with linoleic acid and polyphenol oxidase activity with catechol substrates, in coffee plants damaged (T1) and not damaged (T2) by L. coffeella. L. coffeella digestive enzyme activity was verified by trypsin‐like (substrate l ‐BApNA and l ‐TAME), chymotrypsin‐like (BTpNA and ATEE), cysteine proteases (l ‐BApNA) and total protease (azocasein). Proteinase inhibitor production and lipoxygenase and polyphenol oxidase activity in C. arabica increases (P ≤ 0.05) with L. coffeella damage. Our results provide important information that these enzymatic activities may play a role in plant defence processes in C. arabica. Trypsin‐like activity increases, whereas chymotrypsin‐like and cysteine protease activity decrease in the midgut of L. coffeella, which acts as a defence mechanism.     

Global genetic diversity of Aedes aegypti

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti from 30 countries in six continents, and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co‐occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya), the two subspecies remain genetically distinct, whereas in urban settings, they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats and low migration rates. Ancestral populations in sub‐Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans‐Atlantic shipping in the 16th to 18th centuries was followed by its introduction to Asia in the late 19th century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for the methods using genetic modification of populations.     

Characterization and chromosomal distribution of satellite DNA sequences of the water buffalo (Bubalus bubalis).

Satellite DNA sequences were isolated from the water buffalo (Bubalus bubalis) after digestion with two restriction endonucleases, BamHI and StuI. These satellite DNAs of the water buffalo were classified into two types by sequence analysis: one had an approximately 1,400 bp tandem repeat unit with 79% similarity to the bovine satellite I DNA; the other had an approximately 700 bp tandem repeat unit with 81% similarity to the bovine satellite II DNA. The chromosomal distribution of the satellite DNAs were examined in the river-type and the swamp-type buffaloes with direct R-banding fluorescence in situ hybridization. Both the buffalo satellite DNAs were localized to the centromeric regions of all chromosomes in the two types of buffaloes. The hybridization signals with the buffalo satellite I DNA on the acrocentric autosomes and X chromosome were much stronger than that on the biarmed autosomes and Y chromosome, which corresponded to the distribution of C-band-positive centromeric heterochromatin. This centromere-specific satellite DNA also existed in the interstitial region of the long arm of chromosome 1 of the swamp-type buffalo, which was the junction of the telomere-centromere tandem fusion that divided the karyotype in the two types of buffaloes. The intensity of the hybridization signals with buffalo satellite II DNA was almost the same over all the chromosomes, including the Y chromosome, and no additional hybridization signal was found in noncentromeric sites.     

Song- and order-selective neurons develop in the songbird anterior forebrain during vocal learning

The anterior forebrain (AF) pathway of songbirds has an essential but poorly understood function during song learning, a process requiring auditory experience. Consistent with a role in processing auditory information, two nuclei of the AF, the lateral magnocellular nucleus of the anterior neostriatum (lMAN) and Area X (X), contain some of the most complex auditory neurons known. In adult zebra finches, these neurons are strongly selective for both spectral and temporal properties of song: They respond more robustly to the bird's own song (BOS) than to songs of conspecific individuals, and they respond less well to BOS if it is played in reverse. lMAN and X neurons of young finches early in the process of song learning (30–45 days of age) are also song responsive, but lack the song and order selectivity present in adult birds. By an intermediate stage of learning (60 days), when birds have experience of both tutor song and their own developing (plastic) song, AF neurons have significant song and order selectivity for both tutor song and BOS (in this case, plastic song). The degree of BOS selectivity is still less than that found in adults, however. In addition, neurons at 60 days are heterogenous in their preference for BOS versus tutor song: Most prefer BOS, some prefer tutor song, and others respond equally to both songs. The selectivity of adult AF auditory neurons therefore arises rapidly during development from neurons that are initially unselective. These neurons are one of the clearest examples of experience-dependent acquisition of complex stimulus selectivity. Moreover, the neural selectivity for both BOS and tutor song at 60 days raises the possibility that experience of both songs during learning contributes to the properties of individual AF neurons. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 694–709, 1997     

Post‐flowering night respiration and altered sink activity account for high night temperature‐induced grain yield and quality loss in rice (Oryza sativa L.)

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT‐induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field‐based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post‐flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post‐flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn‐mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT‐induced damage under future warming scenarios.     

Effects of linker length and flexibility on multivalent targeting

Increasing valence can enhance the ability of molecular targeting constructs to bind specifically to targeted cells for drug delivery. Here, we mathematically model the length and flexibility of a linker used to conjoin two peptide ligands of a divalent targeting construct and investigate the influence both on binding avidity and specificity. Four different models are used to approximate varying degrees of linker flexibility (random coil, rigid rod, jointed rods, and combined rod-random coil) and for each linker a binding enhancement factor (VR) is derived that quantifies the increased rate of each construct's second binding event over the first. Results indicate that the moderately flexible models can best reproduce experimentally measured avidities. Also, the magnitude of VR, in conjunction with receptor density and ligand concentration, significantly influences the achievable specificity. Thus, the model elucidates important considerations in designing multivalent targeting constructs for use in delivery of targeted therapy or imaging.     

Growth of the Pacific jack Caranx caninus (Pisces: Carangidae) from the coast of Colima, México

The Pacific jack Caranx caninus is a common species fished by artisanal fishermen off the coast of Colima, México. During 2002, monthly samples of morphometric data and otoliths were taken to determine age and growth. Seven age groups were identified. The highest growth, 14.4 cm, takes place during the first year of life. During the second year, C caninus grows 11.76 cm; the third year 9.61 cm; the fourth 7.85 cm; the fifth 6.41 cm and sixth year 5.24 cm. The constants of von Bertalanffy's growth equation were: L(infinity) = 83.26 cm, W(infinity) = 18.138 g, K = 0.202, t(0) = -0.283 and A(0.95) = 15 years. Growth curves of other species of the same genus were calculated in order to compare them with the one obtained in the present work. The gonadosomatic index presented higher values during November and May. The periods of more intensive feeding are from August to February.     

Use of Bacterially Expressed dsRNA to Downregulate Entamoeba histolytica Gene Expression

Background

Modern RNA interference (RNAi) methodologies using small interfering RNA (siRNA) oligonucleotide duplexes or episomally synthesized hairpin RNA are valuable tools for the analysis of gene function in the protozoan parasite Entamoeba histolytica. However, these approaches still require time-consuming procedures including transfection and drug selection, or costly synthetic molecules.

Principal Findings

Here we report an efficient and handy alternative for E. histolytica gene down-regulation mediated by bacterial double-stranded RNA (dsRNA) targeting parasite genes. The Escherichia coli strain HT115 which is unable to degrade dsRNA, was genetically engineered to produce high quantities of long dsRNA segments targeting the genes that encode E. histolytica β-tubulin and virulence factor KERP1. Trophozoites cultured in vitro were directly fed with dsRNA-expressing bacteria or soaked with purified dsRNA. Both dsRNA delivery methods resulted in significant reduction of protein expression. In vitro host cell-parasite assays showed that efficient downregulation of kerp1 gene expression mediated by bacterial dsRNA resulted in significant reduction of parasite adhesion and lytic capabilities, thus supporting a major role for KERP1 in the pathogenic process. Furthermore, treatment of trophozoites cultured in microtiter plates, with a repertoire of eighty-five distinct bacterial dsRNA segments targeting E. histolytica genes with unknown function, led to the identification of three genes potentially involved in the growth of the parasite.

Conclusions

Our results showed that the use of bacterial dsRNA is a powerful method for the study of gene function in E. histolytica. This dsRNA delivery method is also technically suitable for the study of a large number of genes, thus opening interesting perspectives for the identification of novel drug and vaccine targets.     

Trichoderma theobromicola and T. paucisporum: two new species isolated from cacao in South America

Trichoderma theobromicola and T. paucisporum spp. nov. are described. Trichoderma theobromicola was isolated as an endophyte from the trunk of a healthy cacao tree (Theobroma cacao, Malvaceae) in Amazonian Peru; it sporulates profusely on common mycological media. Trichoderma paucisporum is represented by two cultures that were obtained in Ecuador from cacao pods partially infected with frosty pod rot, Moniliophthora roreri; it sporulates sporadically and most cultures remain sterile on common media and autoclaved rice. It sporulates more reliably on synthetic low-nutrient agar (SNA) but produces few conidia. Trichoderma theobromicola was reintroduced into cacao seedlings through shoot inoculation and was recovered from stems but not from leaves, indicating that it is an endophytic species. Both produced a volatile/diffusable antibiotic that inhibited development of M. roreri in vitro and on-pod trials. Neither species demonstrated significant direct in vitro mycoparasitic activity against M. roreri.