Evolution of the Adh locus in the Drosophila willistoni group: the loss of an intron, and shift in codon usage

We report here the DNA sequence of the alcohol dehydrogenase gene (Adh) cloned from Drosophila willistoni. The three major findings are as follows: (1) Relative to all other Adh genes known from Drosophila, D. willistoni Adh has the last intron precisely deleted; PCR directly from total genomic DNA indicates that the deletion exists in all members of the willistoni group but not in any other group, including the closely related saltans group. Otherwise the structure and predicted protein are very similar to those of other species. (2) There is a significant shift in codon usage, especially compared with that in D. melanogaster Adh. The most striking shift is from C to U in the wobble position (both third and first position). Unlike the codon-usage-bias pattern typical of highly biased genes in D. melanogaster, including Adh, D. willistoni has nearly 50% G + C in the third position. (3) The phylogenetic information provided by this new sequence is in agreement with almost all other molecular and morphological data, in placing the obscura group closer to the melanogaster group, with the willistoni group farther distant but still clearly within the subgenus Sophophora.      

Slipped-strand mispairing in a plastid gene: rpoC2 in grasses (Poaceae)

An exception to the generally conservative nature of plastid gene evolution is the gene coding for the beta" subunit of RNA polymerase, rpoC2. Previous work by others has shown that maize and rice have an insertion in the coding region of rpoC2, relative to spinach and tobacco. To assess the distribution of this extra coding sequence, we surveyed a broad phylogenetic sample comprising 55 species from 17 angiosperm families by using Southern hybridization. The extra coding sequence is restricted to the grasses (Poaceae). DNA sequence analysis of 11 species from all five subfamilies within the grass family demonstrates that the extra sequence in the coding region of rpoC2 is a repetitive array that exhibits more than a twofold increase in nucleotide substitution, as well as a large number of insertion/deletion events, relative to the adjacent flanking sequences. The structure of the array suggests that slipped-strand mispairing causes the repeated motifs and adds to the mechanisms through which the coding sequence of plastid genes are known to evolve. Phylogenetic analyses based on the sequence data from grass species support several relationships previously suggested by morphological work, but they are ambiguous about broad relationships within the family.      

Bacteria of the <Emphasis Type="Italic">Burkholderia cepacia</Emphasis> complex are cyanogenic under biofilm and colonial growth conditions

Background  

The Burkholderia cepacia complex (Bcc) is a collection of nine genotypically distinct but phenotypically similar species. They show wide ecological diversity and include species that are used for promoting plant growth and bio-control as well species that are opportunistic pathogens of vulnerable patients. Over recent years the Bcc have emerged as problematic pathogens of the CF lung. Pseudomonas aeruginosa is another important CF pathogen. It is able to synthesise hydrogen cyanide (HCN), a potent inhibitor of cellular respiration. We have recently shown that HCN production by P. aeruginosa may have a role in CF pathogenesis. This paper describes an investigation of the ability of bacteria of the Bcc to make HCN.     

Thigmo responses in plants and fungi

Thigmo mechanisms are adaptations that permit a plant to alter growth rates, change morphology, produce tropisms, avoid barriers, control germination, cling to supporting structures, infect a host plant, facilitate pollination, expedite the movement of pollen, spores, or seeds, and capture prey. Through these varied functions, plant thigmo systems have evolved impressive controls of cell differentiation, localized growth rates, regulated synthesis of novel products, and some elegant traps and projectile systems. For most thigmo events, there will be a dependence upon transmission of a signal from the cell wall through the plasmalemma and into the cytoplasm. We propose the possible involvement of integrin-like proteins, Hechtian strands, and cytoskeletal structures as possible transduction components. Many thigmo mechanisms may use some modification of the calcium/calmodulin signal transduction system, though the details of transduction systems are still poorly understood. While transmission of thigmo signals to remote parts of a plant is associated with the development of action potentials, hormones may also play a role. Thigmo mechanisms have facilitated an enormous array of plant and fungal adaptations that make major contributions to their success despite their relatively sessile or immobile states.     

Mg2+ blocks myogenic tone but not K+-induced constriction: role for SOCs in small arteries

The effects of Mg(2+) and nifedipine (Nif) on vasoconstriction and Ca(2+) transients were studied in intact, pressurized rat mesenteric arteries with myogenic tone. Changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) were measured with confocal microscopy in fluo 4-AM loaded, individual myocytes. Myogenic tone was abolished by 10 mM Mg(2+) or 0.3 microM Nif. Contractions induced by 75 mM K(+) depolarization were blocked by 0.3 microM Nif, but not by 10 mM Mg(2+). Phenylephrine (PE; 5 microM) evoked sustained [Ca(2+)](cyt) elevation and vasoconstriction with superimposed Ca(2+) oscillations and vasomotion. The subsequent addition of 10 mM Mg(2+) or 0.3 microM Nif reduced [Ca(2+)](cyt) and abolished plateau vasoconstriction. When added before PE, both Mg(2+) and Nif abolished the PE-evoked Ca(2+) oscillations and vasomotion. Mg(2+) dilated the PE-constricted arteries after a brief (< or =180-240 s) vasoconstriction, but Nif did not. Both agents also abolished the vasoconstriction attributed to Ca(2+) entry through store-operated channels (SOCs) during internal Ca(2+) store refilling that followed store depletion. The data suggest that Ca(2+) entry through SOCs helps maintain both myogenic tone and alpha(1)-adrenoceptor-induced tonic vasoconstriction.     

Left sided ablation for Atrioventricular Nodal Re-entrant Tachycardia: Frequency,Characteristics and Outcomes

BackgroundLeft-sided ablation, targeting left inferior AV nodal extensions, is thought to be necessary for success in a small proportion of atrioventricular nodal re-entrant tachycardia (AVNRT) ablations; however Indian data are scarce in this regard.MethodsConsecutive cases of AVNRT undergoing slow pathway ablation in a single centre over an 18-month period were retrospectively analyzed. Left-sided ablation at the posteroseptal mitral annulus was performed if right-sided ablation failed to abolish AVNRT.ResultsFrom January 2017 to June 2018, out of 215 consecutive supraventricular tachycardia (SVT) cases, 154 (71.6%) were AVNRT (47.1 ± 13.1 years, 46.1% male). Trans-septal ablation was required in 5 (3.2%) cases (mean age 48.8 ± 9.4 years; 4 female, 1 male); all with typical (slow-fast) form of AVNRT. Compared with cases needing only right-sided ablation, radiofrequency time (50.8 ± 16.9 vs. 9.9 ± 8.5 min; p = 0.005) and procedure time (166.0 ± 35.0 vs 79.6 ± 35.9 min; p = 0.004) were significantly longer for trans-septal cases, while baseline intervals and tachycardia cycle length were not significantly different. Junctional ectopy was seen in only 2 of the 5 cases during left-sided ablation, but acute success (non-inducibility) was obtained in 3 cases. There were no instances of AV block. Over mean follow-up of 12.2 ± 4.0 months, clinical recurrence of AVNRT occurred in one case, while others remained arrhythmia-free without medication.ConclusionLeft-sided ablation was required in a small proportion of AVNRT ablations. Trans-septal approach targeting the posteroseptal mitral annulus was safe and yielded good mid-term clinical success.     

Dyssynchronous Ventricular Activation in Asymptomatic Wolff-Parkinson-White Syndrome: A Risk Factor for Development of Dilated Cardiomyopathy

A subset of children and adults with Wolff-Parkinson-White (WPW) syndrome develop dilated cardiomyopathy (DCM). Although DCM may occur in symptomatic WPW patients with sustained tachyarrhythmias, emerging evidence suggests that significant left ventricular dysfunction may arise in WPW in the absence of incessant tachyarrhythmias. An invariable electrophysiological feature in this non-tachyarrhythmia type of DCM is the presence of a right-sided septal or paraseptal accessory pathway. It is thought that premature ventricular activation over these accessory pathways induces septal wall motion abnormalities and ventricular dyssynchrony. LV dyssynchrony induces cellular and structural ventricular remodelling, which may have detrimental effects on cardiac performance. This review summarizes recent evidence for development of DCM in asymptomatic patients with WPW, discusses its pathogenesis, clinical presentation, management and treatment. The prognosis of accessory pathway-induced DCM is excellent. LV dysfunction reverses following catheter ablation of the accessory pathway, suggesting an association between DCM and ventricular preexcitation. Accessory pathway-induced DCM should be suspected in all patients presenting with heart failure and overt ventricular preexcitation, in whom no cause for their DCM can be found.     

Pith Autolysis in Plants: IV. The Activity of Polygalacturonase and Cellulase during Drought Stress Induced Pith Autolysis

The water potential, amount of pith autolysis and activitiesof apoplastic cellulase and polygalacturonase of tomato stemswere measured during 24 h of drought stress (DS) and for 24h following reirrigation. During DS the water potential droppedfrom —5.5 to —10.4 bars and rose to —8.3 barssoon after reirrigation. Drought stress induced considerablepith autolysis, more of which occurred after reirrigation. Pretreatmentwith mechanical perturbation (MP) of the stems or applicationof exogenous ethephon on the buds hardened the tomato plantsagainst DS-induced pith autolysis. Drought stress caused anincrease in apoplastic polygalacturonase and an even greaterincrease in apoplastic cellulase. Reirrigation caused a largetransient increase in the former and a decrease in the latter.The apoplastic reducing sugar content (as galacturonic acid)of the stem rose in parallel with the activity of the enzymes.Both DS and MP caused an increase in ethylene evolution, althoughthe former was significantly greater than the latter. However,when MP preceded DS, the amount of ethylene produced was significantlyless than DS alone induced. Pretreatment with either MP or exogenousethephon inhibited the increase in apoplastic cellulytic enzymes. It is concluded that DS induces ethylene evolution from thetomato stem, causing an increase in the stem apoplastic cellulyticenzymes, which in turn start the autolysis of the pith cellwalls. Pretreatment with MP or ethephon, each of which inducesethylene evolution, hardens the stem so that it does not producemore ethylene during DS, and thus becomes resistant to DS-inducedpith autolysis. ¹Supported by Bi-national Agricultural Research and Developmentgrant I-127, NASA grant NAGW 96 and NSF grant 8003689to MJJ. ²Permanent address: Horticulture Department, Faculty of Agriculture,The Hebrew University Rehovot, Israel ³Permanent address: Vegetable Crops Department, AgriculturalResearch Organization, the Volcani Center Bet Dagan, Israel