A potential cyanobacterial ancestor of Viridiplantae chloroplasts

The theory envisaging the origin of plastids from endosymbiotic cyanobacteria is well-established but it is difficult to explain the evolution (spread) of plastids in phylogenetically diverse plant groups. It is widely believed that primordial endosymbiosis occurred in the last common ancestor of all algae^1^, which then diverged into the three primary photosynthetic eukaryotic lineages, viz. the Rhodophyta (red algae), Glaucocystophyta (cyanelle-containing algae) and Viridiplantae (green algae plus all land plants)^2^. Members of these three groups invariably have double membrane-bound plastids^3^, a property that endorses the primary endosymbiotic origin of the organelles. On the other hand, the three or four membrane-bound plastids of the evolutionary complicated Chromalveolates [chromista (cryptophytes, haptophytes, and stramenopiles) and alveolata (dinoflagellates, apicomplexans, and ciliates)] are inexplicable in the light of a single endosymbiosis event, thereby necessitating the postulation of the secondary^4,5^ and tertiary^6^ endosymbiosis theories where a nonphotosynthetic protist supposedly engulfed a red or a green alga^7^ and an alga containing a secondary plastid itself was engulfed^8^ respectively. In the current state of understanding, however, there is no clue about the taxonomic identity of the cyanobacterial ancestor of chloroplasts, even though there is a wide consensus on a single primordial endosymbiosis event. During our metagenomic investigation of a photosynthetic geothermal microbial mat community we discovered a novel order-level lineage of Cyanobacteria that - in 16S rRNA gene sequence-based phylogeny - forms a robust monophyletic clade with chloroplast-derived sequences from diverse divisions of Viridiplantae. This cluster diverged deeply from the other major clade encompassing all hitherto known groups of Cyanobacteria plus the chloroplasts of Rhodophyta, Glaucocystophyceae and Chromalveolates. Since this fundamental dichotomy preceded the origin of all chloroplasts, it appears that two early-diverging cyanobacterial lineages had possibly given rise to two discrete chloroplast descents via two separate engulfment events

Sudden warming epochs during 42 to 28 ky bp in the Himalayan region from stable iso-tope record of sediment column from a relict lake in Goting, Garhwal, North India

18O/16O variations of the precipitation recorded in carbonate sediments of a high-altitude Himalayan lake have been investigated by analysing samples from a varve deposit in Goting, Garhwal Himalaya. 14C ages of four samples from different depths suggest that the sedimentation in the lake started ~ 42 ky BP and continued till ~ 28 ky BP. Fluctuations in δ18O values are interpreted in terms of water-source variations. A trend showing the enrichment of δ18O values between 32 and 28 ka indicates slow cooling as one approaches the Last Glacial Maximum (LGM). There are six strong δ18O excursions (depleted ratios) coinciding with low 13C values at around 40.2, 38.2, 36.2, 34.2, 32.8 and 29.4 ky BP, denoting enhancement of the southwest monsoon. In addition, three positive shifts at around 40.7, 37.2 and 35.2 ky BP were observed, which indicate weakening of the southwest monsoon. Fourier analysis of the δ18O time series shows a significant ~ 740 year periodicity, similar to that reported in the Arabian Sea and South China Sea

Negative &#948;<SUP>13</SUP>C excursion and anoxia at the Permo-Triassic boundary in the Tethys Sea

The Permian-Triassic (P-T) sections in Spiti valley, Himalaya represent sedimentary deposits of a shallow sea and show a sharp negative transition of &#948; 13C in total organic matter, kerogen fraction and carbonate phase. This excursion occurs across the upper part of the Permian shale culminating in a ferruginous band, which marks the peak of anoxicity after a period of generally low-oxygenated condition in the basin, as inferred on the basis of trace element analysis. Presence of carbon isotopic shift along with anoxia is similar to that observed in many P-T sections over the globe and suggests that Permo-Triassic transitional records of the Neo-Tethys are preserved in the ferruginous band of the Spiti valley sections

Trace element and isotopic studies of Permo-Carboniferous carbonate nodules from Talchir sediments of peninsular India: environmental and provenance implications

Syngenetic carbonate nodules constitute an interesting feature of the glaciogene sediments of various Talchir basins in peninsular India. Petrographic, cathodoluminescence and sedimentary results suggest that many of these nodules contain primary carbonate precipitates whose geochemical signatures can be used for determining environment of deposition and provenance of the sediments and drainage source. Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean δ18O and δ13C values of the calcites in the nodules are - 19.5% and-9.7% (w.r.t. PDB) respectively suggesting a freshwater environment (probably lacustrine) for formation of these objects. Trace element ratios (Eu/Eu* and La/Yb) of the nodule samples show that the source of the sediments in the Damodar valley basin was the granites, gneisses and intrusives in the Chotanagpur region. The sediments in the Mahanadi valley were derived from granulites, charnockites and granites of the eastern ghat region. The Sr concentration of the carbonate phase of the nodules is low, ranging from 10-60 ng/g. The87Sr/86Sr ratios of the samples from the west Bokaro basin and Ramgarh basin vary from 0.735 to 0.748 (mean: 0.739) and from 0.726 to 0.733 (mean: 0.730) respectively. These values are consistent with our proposition that water of these basins drained through the granitic rocks of the Chotanagpur region. In contrast, the87Sr/86Sr ratios of the samples from the Talchir basin (Type area) of Mahanadi valley vary from 0.718 to 0.723 (mean: 0.719). These87Sr/86Sr ratios are close to those of the granulites in the adjoining eastern ghat belt suggesting that area as the drainage source

Potential Role of Brain-Derived Neurotrophic Factor and Dopamine Receptor D2 Gene Variants as Modifiers for the Susceptibility and Clinical Course of Wilson's Disease

Wilson's disease (WD), an inborn error of copper metabolism caused by mutations in the ATPase copper transporting beta (ATP7B) gene, manifests variable age of onset and different degrees of hepatic and neurological disturbances. This complex phenotypical outcome of a classical monogenic disease can possibly be explained by modifier loci regulating the clinical course of the disease. The brain-derived neurotropic factor (BDNF), critical for the survival, morphogenesis, and plasticity of the neurons, and the dopamine receptor D2 (DRD2), one of the most abundant dopamine receptors in the brain, have been highlighted in the pathophysiology of various neuropsychiatric diseases. This study aims to identify the potential association between BDNF and DRD2 gene polymorphisms and WD and its clinical characteristics. A total of 164 WD patients and 270 controls from India were included in this study. Two BDNF polymorphisms [p.Val66Met (c.G196A) and c.C270T] and the DRD2 Taq1A (A2/A1 or C/T) polymorphism were examined for their association with WD and some of its clinical attributes, using polymerase chain reaction, restriction fragment length digestion, and bidirectional sequencing. The C allele and CC genotype of BDNF C270T were significantly overrepresented among controls compared to WD patients. In addition, a significantly higher proportion of the allele coding for Val and the corresponding homozygous genotype of BDNF Val66Met polymorphism was found among WD patients with age of onset later than 10 years. Furthermore, the A1A1 genotype of DRD2 Taq1A polymorphism was significantly more common among WD patients with rigidity. Our data suggest that both BDNF and DRD2 may act as potential modifiers of WD phenotype in the Indian context.</p