The early evolution of life: solution to Darwin's dilemma

Recent studies of Precambrian fossils indicate that life on Earth originated earlier than assumed, microscopic life was prevalent in the Precambrian Eon, the tempo and mode of evolution during the Precambrian period were different from other periods, and that only the Precambrian fossil record can be used as evidence of early life. Implications for future research include directing the search for the origin of life away from the geological record, modification of hypotheses about molecular change, use of Precambrian microfossils in dating younger geological units, and progress in defining the nature of major events in early evolution.     

Regulation of growth by the trehalose pathway: Relationship to temperature and sucrose

Carbon signaling can override carbon supply in the regulation of growth. At least some of this regulation is imparted by the sugar signal trehalose 6-phosphate (T6P) through the protein kinase, SnRK1. This signaling pathway regulates biosynthetic processes involved in growth under optimal growing conditions. Recently, using a seedling system we showed that under sub-optimal conditions, such as cold, carbon signaling by T6P/ SnRK1 enables recovery of growth following relief of the stress. The T6P/ SnRK1 mechanism thus could be selected as a means of improving low temperature tolerance. High-throughput automated Fv/Fm measurements provide a potential means to screen for T6P/ SnRK1, and here we confirm through measurements of Fv/Fm in rosettes that T6P promotes low temperature tolerance and recovery during cold to warm transfer. Further, to better understand the coordination between sugars, trehalose pathway, and temperature-dependent growth, we examine the interrelationship between sugars, trehalose phosphate synthase (TPS), and trehalose phosphate phosphatase (TPP) gene expression and T6P content in seedlings. Sucrose, particularly when fed exogenously, correlated well with TPS1 and TPPB gene expression, suggesting that these enzymes are involved in maintaining carbon flux through the pathway in relation to sucrose supply. However, when sucrose accumulated to higher levels under low temperature and low N, TPS1 and TPPB expression were less directly related to sucrose; other factors may also contribute to regulation of TPS1 and TPPB expression under these conditions. TPPA expression was not related to sucrose content and all genes were not well correlated with endogenous glucose. Our work has implications for understanding acclimation to sink-limited growth conditions such as low temperature and for screening cold-tolerant genotypes with altered T6P/ SnRK1 signaling.     

Draft genome sequence of Sinorhizobium meliloti RU11/001, a model organism for flagellum structure,motility and chemotaxis

Sinorhizobium meliloti of the order Rhizobiales is a symbiotic nitrogen-fixing bacterium nodulating plants of the genera Medicago, Trigonella and Melilotus and hence is of great agricultural importance. In its free-living state it is motile and capable of modulating its movement patterns in response to chemical attractants. Here, the draft genome consisting of a circular chromosome, the megaplasmids pSymA and pSymB and three accessory plasmids of Sinorhizobium meliloti RU11/001, a model organism for flagellum structure, motility and chemotaxis, is reported.     

Heat stress reveals a specialized variant of the pachytene checkpoint in meiosis of Arabidopsis thaliana

Plant growth and fertility strongly depend on environmental conditions such as temperature. Remarkably, temperature also influences meiotic recombination and thus, the current climate change will affect the genetic make-up of plants. To better understand the effects of temperature on meiosis, we followed male meiocytes in Arabidopsis thaliana by live cell imaging under three temperature regimes: at 21°C; at heat shock conditions of 30°C and 34°C; after an acclimatization phase of 1 week at 30°C. This work led to a cytological framework of meiotic progression at elevated temperature. We determined that an increase from 21°C to 30°C speeds up meiosis with specific phases being more amenable to heat than others. An acclimatization phase often moderated this effect. A sudden increase to 34°C promoted a faster progression of early prophase compared to 21°C. However, the phase in which cross-overs mature was prolonged at 34°C. Since mutants involved in the recombination pathway largely did not show the extension of this phase at 34°C, we conclude that the delay is recombination-dependent. Further analysis also revealed the involvement of the ATAXIA TELANGIECTASIA MUTATED kinase in this prolongation, indicating the existence of a pachytene checkpoint in plants, yet in a specialized form.

Live cell imaging of plants exposed to different heat stresses provides a temporal framework of meiosis at high temperatures in wild-type and mutants for several meiotic recombination factors.     

Effects of Glyptapanteles liparidis (Hym.: Braconidae) parasitism, polydnavirus, and venom on development of microsporidia-infected and uninfected Lymantria dispar (Lep.: Lymantriidae) larvae

Effects of parasitism, polydnavirus, and venom of the endoparasitoid Glyptapanteles liparidis on Lymantria dispar larvae infected with the microsporidium Vairimorpha sp. and uninfected hosts were studied. We tested the impact on growth and development of hosts, as well as on microsporidian infection. Both parasitism and polydnavirus/venom treatment alone caused a slight increase in growth rate and relative growth rate in uninfected fourth instar hosts. This effect was more pronounced with the addition of Vairimorpha infection. With no parasitism, however, infection reduced host growth markedly. Microsporidiosis delayed larval molts of L. dispar, and additional polydnavirus/venom treatment or parasitization induced significantly earlier molting. Polydnavirus/venom treatment of uninfected L. dispar resulted in prolonged larval development due to supernumerary molts and in higher pupal mortality. Infected larvae treated with polydnavirus/venom died earlier than infected larvae that were not treated and produced more Vairimorpha spores per unit fresh mass of the host.     

Abi1 is essential for the formation and activation of a WAVE2 signalling complex

WAVE2 belongs to a family of proteins that mediates actin reorganization by relaying signals from Rac to the Arp2/3 complex, resulting in lamellipodia protrusion. WAVE2 displays Arp2/3-dependent actin nucleation activity in vitro, and does not bind directly to Rac. Instead, it forms macromolecular complexes that have been reported to exert both positive and negative modes of regulation. How these complexes are assembled, localized and activated in vivo remains to be established. Here we use tandem mass spectrometry to identify an Abi1-based complex containing WAVE2, Nap1 (Nck-associated protein) and PIR121. Abi1 interacts directly with the WHD domain of WAVE2, increases WAVE2 actin polymerization activity and mediates the assembly of a WAVE2-Abi1-Nap1-PIR121 complex. The WAVE2-Abi1-Nap1-PIR121 complex is as active as the WAVE2-Abi1 sub-complex in stimulating Arp2/3, and after Rac activation it is re-localized to the leading edge of ruffles in vivo. Consistently, inhibition of Abi1 by RNA interference (RNAi) abrogates Rac-dependent lamellipodia protrusion. Thus, Abi1 orchestrates the proper assembly of the WAVE2 complex and mediates its activation at the leading edge in vivo.     

Quantitative analysis of micro-CT imaging and histopathological signatures of experimental arthritis in rats

Micro-computed tomographic (micro-CT) imaging provides a unique opportunity to capture 3-D architectural information in bone samples. In this study of pathological joint changes in a rat model of adjuvant-induced arthritis (AA), quantitative analysis of bone volume and roughness were performed by micro-CT imaging and compared with histopathology methods and paw swelling measurement. Micro-CT imaging of excised rat hind paws (n = 10) stored in formalin consisted of approximately 600 30-mum slices acquired on a 512 x 512 image matrix with isotropic resolution. Following imaging, the joints were scored from H&E stained sections for cartilage/bone erosion, pannus development, inflammation, and synovial hyperplasia. From micro-CT images, quantitative analysis of absolute bone volumes and bone roughness was performed. Bone erosion in the rat AA model is substantial, leading to a significant decline in tarsal volume (27%). The result of the custom bone roughness measurement indicated a 55% increase in surface roughness. Histological and paw volume analyses also demonstrated severe arthritic disease as compared to controls. Statistical analyses indicate correlations among bone volume, roughness, histology, and paw volume. These data demonstrate that the destructive progression of disease in a rat AA model can be quantified using 3-D micro-CT image analysis, which allows assessment of arthritic disease status and efficacy of experimental therapeutic agents.