Analysis of phytochrome-deficient yellow-green-2 and aurea mutants of tomato

Two alleles of the yellow-green-2 ( yg-2) and eight different alleles of the aurea ( au ) locus of tomato ( Lycopersicon esculentum Mill.) were compared. All are characterized by a paler green colour compared with wild-type (WT), an elongated hypocotyl in red light, and low or below detection limits of spectrophotometrically active phytochrome. Hypocotyl length was variable in white light, ranging from that of WT to more elongated. Immunochemical analysis revealed that etiolated seedlings of the yg-2 mutant have approximately 25% of the WT level of phytochrome A protein (PHYA), whereas that of phytochrome B protein (PHYB) is normal. In this it resembles the au mutant. The au,yg-2 double mutant has a more extreme chlorophyll deficiency than either parent. Since the yg-2 and au mutants have a less severe phenotype at the adult stage, that is, are leaky, the additive effect can be explained by assuming that the mutants control two steps in the chromophore biosynthesis pathway. Combination, by crossing, of the yg-2 and au mutants with a transgenic tomato line that overexpresses oat phytochrome A3 (PhyA-3) essentially failed to restore the WT phenotype under white fluorescent light conditions, although under greenhouse conditions some evidence for increased sensitivity to light was observed. Immunochemically, oat PHYA-3 protein is detectable in both the yg-2,PhyA-3 and au,PhyA-3 'double' mutants. Spectrophotometrical analysis, however, revealed that holophytochrome was undetectable in the yg-2,PhyA-3 and au,PhyA-3 'double' mutants. These results are compatible with both mutants being disturbed in phytochrome chromophore biosynthesis.     

Localization of the human thyroxine-binding globulin gene to the long arm of the X chromosome (Xq21-22).

Thyroxine-binding globulin (TBG) is the major thyroid-hormone transport protein in the plasma of most vertebrate species. A recombinant phage (lambda cTBG8) containing a cDNA insert of human TBG recently has been described. With the cDNA insert from lambda cTBG8 used as a radiolabeled probe, DNA from a series of somatic-cell hybrids containing deletions of the X chromosome was analyzed by means of blot hybridization. The results indicated that the TBG gene is located in the midportion of the long arm of the X chromosome between bands Xq11 and Xq23. The gene then was mapped to band region Xq21-22 by means of in situ hybridization to metaphase chromosomes. Sequences on the X chromosome that are homologous to the cDNA probe are contained within a single EcoRI restriction fragment of 12.5 kb in human DNA. On the basis of the intensity of the hybridization signal on Southern blots, it was determined that the human TBG cDNA probe used in the present study shares significant homology with hamster and mouse sequences. A single EcoRI restriction fragment was recognized in both hamster (8.0-kb) and mouse (5.1-kb) DNA.     

Agroecology: the key role of arbuscular mycorrhizas in ecosystem services

The beneficial effects of arbuscular mycorrhizal (AM) fungi on plant performance and soil health are essential for the sustainable management of agricultural ecosystems. Nevertheless, since the ‘first green revolution’, less attention has been given to beneficial soil microorganisms in general and to AM fungi in particular. Human society benefits from a multitude of resources and processes from natural and managed ecosystems, to which AM make a crucial contribution. These resources and processes, which are called ecosystem services, include products like food and processes like nutrient transfer. Many people have been under the illusion that these ecosystem services are free, invulnerable and infinitely available; taken for granted as public benefits, they lack a formal market and are traditionally absent from society’s balance sheet. In 1997, a team of researchers from the USA, Argentina and the Netherlands put an average price tag of US $33 trillion a year on these fundamental ecosystem services. The present review highlights the key role that the AM symbiosis can play as an ecosystem service provider to guarantee plant productivity and quality in emerging systems of sustainable agriculture. The appropriate management of ecosystem services rendered by AM will impact on natural resource conservation and utilisation with an obvious net gain for human society.     

Calibration and error in placental molecular clocks: a conservative approach using the cetartiodactyl fossil record

The nature of the molecular and fossil record and their limitations must be ascertained in order to gain the most precise and accurate evolutionary timescale using genetic information. Yet the majority of such timescales are based on point estimates using fossils or the molecular clock. Here we document from the primary literature minimum and maximum fossil age estimates of the divergence of whales from artiodactyls, a commonly used anchor point for calibrating both mitogenomic and nucleogenomic placental timescales. We applied these reestimates to the most recently established placental timescale based on mitochondrial rRNA and several nuclear loci, and present an attempt to account for both genetic and fossil uncertainty. Our results indicate that disregard for fossil calibration error may inflate the power of the molecular clock when testing the time of ordinal diversification in context with the K-T boundary. However, the early history of placentals, including their superordinal diversification, remained in the Cretaceous despite a conservative approach. Our conclusions need corroboration across other frequently used fossil anchor points, but also with more genetic partitions on the linear relationship between molecular substitutions and geologic time.     

Calibration of avian molecular clocks

Molecular clocks can be calibrated using fossils within the group under study (internal calibration) or outside of the group (external calibration). Both types of calibration have their advantages and disadvantages. An internal calibration may reduce extrapolation error but may not be from the best fossil record, raising the issue of nonindependence. An external calibration may be more independent but also may have a greater extrapolation error. Here, we used the advantages of both methods by applying a sequential calibration to avian molecular clocks. We estimated a basal divergence within birds, the split between fowl (Galliformes) and ducks (Anseriformes), to be 89.8 +/- 6.97 MYA using an external calibration and 12 rate-constant nuclear genes. In turn, this time estimate was used as an internal calibration for three species-rich avian molecular data sets: mtDNA, DNA-DNA hybridization, and transferrin immunological distances. The resulting time estimates indicate that many major clades of modern birds had their origins within the Cretaceous. This supports earlier studies that identified large gaps in the avian fossil record and suggests that modern birds may have coexisted with other avian lineages for an extended period during the Cretaceous. The new time estimates are concordant with a continental breakup model for the origin of ratites.     

Heterochromatin, synaptonemal complex, and NOR activity in the somatic and germ cells of a male domestic dog, Canis familiaris (Mammalia, Canidae)

C-banding and silver staining of the somatic and germ cells of the male domestic dog. Canis familiaris, have shown that: (1) the amount of C-banding is small compared to most other mammalian species, (2) three pairs of autosomes have nucleolus organizer regions (NORs) at the terminal ends of their long arms, whereas the Y chromosome has an NOR on the terminal end of the short arm, (3) the organization of the synaptonemal complex (SC) is similar to that of other mammalian species, (4) a distinct SC is formed between the long arm of the Y chromosome and probably the short arm of the X chromosome, and (5) the differential axes of both sex chromosomes do not demonstrate fusiform thickenings nor do they stain darkly with silver as do the XY bivalents in many other mammalian species.     

Synthesizing and databasing fossil calibrations: divergence dating and beyond

Divergence dating studies, which combine temporal data from the fossil record with branch length data from molecular phylogenetic trees, represent a rapidly expanding approach to understanding the history of life. National Evolutionary Synthesis Center hosted the first Fossil Calibrations Working Group (3-6 March, 2011, Durham, NC, USA), bringing together palaeontologists, molecular evolutionists and bioinformatics experts to present perspectives from disciplines that generate, model and use fossil calibration data. Presentations and discussions focused on channels for interdisciplinary collaboration, best practices for justifying, reporting and using fossil calibrations and roadblocks to synthesis of palaeontological and molecular data. Bioinformatics solutions were proposed, with the primary objective being a new database for vetted fossil calibrations with linkages to existing resources, targeted for a 2012 launch.