RanGAP2 mediates nucleocytoplasmic partitioning of the NB-LRR immune receptor Rx in the Solanaceae, thereby dictating Rx function

The potato (Solanum tuberosum) nucleotide binding-leucine-rich repeat immune receptor Rx confers resistance to Potato virus X (PVX) and requires Ran GTPase-activating protein 2 (RanGAP2) for effective immune signaling. Although Rx does not contain a discernible nuclear localization signal, the protein localizes to both the cytoplasm and nucleus in Nicotiana benthamiana. Transient coexpression of Rx and cytoplasmically localized RanGAP2 sequesters Rx in the cytoplasm. This relocation of the immune receptor appeared to be mediated by the physical interaction between Rx and RanGAP2 and was independent of the concomitant increased GAP activity. Coexpression with RanGAP2 also potentiates Rx-mediated immune signaling, leading to a hypersensitive response (HR) and enhanced resistance to PVX. Besides sequestration, RanGAP2 also stabilizes Rx, a process that likely contributes to enhanced defense signaling. Strikingly, coexpression of Rx with the Rx-interacting WPP domain of RanGAP2 fused to a nuclear localization signal leads to hyperaccumulation of both the WPP domain and Rx in the nucleus. As a consequence, both Rx-mediated resistance to PVX and the HR induced by auto-active Rx mutants are significantly suppressed. These data show that a balanced nucleocytoplasmic partitioning of Rx is required for proper regulation of defense signaling. Furthermore, our data indicate that RanGAP2 regulates this partitioning by serving as a cytoplasmic retention factor for Rx.     

Quantifying population structure using the F-model

We review a model-based approach to estimate local population F(ST) 's that is based on the multinomial-Dirichlet distribution, the so-called F-model. As opposed to the standard method of estimating a single F(ST) value, this approach takes into account the fact that in most if not all realistic situations, local populations differ in their effective sizes and migration rates. Therefore, the use of this approach can help better describe the genetic structure of populations. Despite this obvious advantage, this method has remained largely underutilized by molecular ecologists. Thus, the objective of this review is to foster its use for studying the genetic structure of metapopulations. We present the derivation of the Bayesian formulation for the estimation of population-specific F(ST) 's based on the multinomial-Dirichlet distribution. We describe several recent applications of the F-model and present the results of a small simulation study that explains how the F-model can help better describe the genetic structure of populations.     

Natural variation in Arabidopsis thaliana revealed a genetic network controlling germination under salt stress

Plant responses to environmental stresses are polygenic and complex traits. In this study quantitative genetics using natural variation in Arabidopsis thaliana was used to investigate the genetic architecture of plant responses to salt stress. Eighty seven A. thaliana accessions were screened and showed a large variation for root development and seed germination under 125 and 200 mM NaCl, respectively. Twenty two quantitative trait loci for these traits have been detected by phenotyping two recombinants inbred line populations, Sha x Col and Sha x Ler. Four QTLs controlling germination under salt were detected in the Sha x Col population. Interestingly, only one allelic combination at these four QTLs inhibits germination under salt stress, implying strong epistatic interactions between them. In this interacting context, we confirmed the effect of one QTL by phenotyping selected heterozygous inbred families. We also showed that this QTL is involved in the control of germination under other stress conditions such as KCl, mannitol, cold, glucose and ABA. Our data highlights the presence of a genetic network which consists of four interacting QTLs and controls germination under limiting environmental conditions.     

Seasonal and Regional Dynamics of M. ulcerans Transmission in Environmental Context: Deciphering the Role of Water Bugs as Hosts and Vectors

Background

Buruli ulcer, the third mycobacterial disease after tuberculosis and leprosy, is caused by the environmental mycobacterium M. ulcerans. Various modes of transmission have been suspected for this disease, with no general consensus acceptance for any of them up to now. Since laboratory models demonstrated the ability of water bugs to transmit M. ulcerans, a particular attention is focused on the transmission of the bacilli by water bugs as hosts and vectors. However, it is only through detailed knowledge of the biodiversity and ecology of water bugs that the importance of this mode of transmission can be fully assessed. It is the objective of the work here to decipher the role of water bugs in M. ulcerans ecology and transmission, based on large-scale field studies.

Methodology/Principal Findings

The distribution of M. ulcerans-hosting water bugs was monitored on previously unprecedented time and space scales: a total of 7,407 water bugs, belonging to large number of different families, were collected over one year, in Buruli ulcer endemic and non endemic areas in central Cameroon. This study demonstrated the presence of M. ulcerans in insect saliva. In addition, the field results provided a full picture of the ecology of transmission in terms of biodiversity and detailed specification of seasonal and regional dynamics, with large temporal heterogeneity in the insect tissue colonization rate and detection of M. ulcerans only in water bug tissues collected in Buruli ulcer endemic areas.

Conclusion/Significance

The large-scale detection of bacilli in saliva of biting water bugs gives enhanced weight to their role in M. ulcerans transmission. On practical grounds, beyond the ecological interest, the results concerning seasonal and regional dynamics can provide an efficient tool in the hands of sanitary authorities to monitor environmental risks associated with Buruli ulcer.     

Sex-specific foraging behaviour in a seabird with reversed sexual dimorphism: the red-footed booby

Most hypotheses attempting to explain the evolution of reversed sexual dimorphism (RSD) assume that size-related differences in foraging ability are of prime importance, but the studies on sex-specific differences in foraging behaviour remain scarce. We compare the foraging behaviour of males and females in a seabird species with a RSD by using several miniaturised activity and telemetry loggers. In red-footed boobies males are 5% smaller and 15% lighter than females, but have a longer tail than females. Both sexes spend similar time on the nest while incubating or brooding. When foraging at sea, males and females spend similar time foraging in oceanic waters, forage in similar areas, spend similar proportion of their foraging trip in flight, and feed on similar prey—flying fishes and flying squids—of similar size. However, compared to males, females range farther during incubation (85 km vs. 50 km), and furthermore feed mostly at the extremity of their foraging trip, whereas males actively forage throughout the trip. Males are much more active than females, landing and diving more often. During the study period, males lost mass, whereas females showed no significant changes. These results indicate that males and females of the red-footed boobies differ in several aspects in their foraging behaviour. Although some differences found in the study may be the direct result of the larger size of females, that is, the slightly higher speeds and deeper depths attained by females, others indicate clearly different foraging strategies between the sexes. The smaller size and longer tail of males confer them a higher agility, and could allow them to occupy a foraging niche different from that of females. The higher foraging effort of males related to its different foraging strategy is probably at the origin of the rapid mass loss of males during the breeding period. These results suggest that foraging differences are probably the reason for the differential breeding investment observed in boobies, and are likely to be involved in the evolution and maintenance of RSD.     

Central nervous system myelin of teleosts: comparative electrophoretic analysis of its proteins by staining and immunoblotting

CNS myelin was isolated from 24 teleostean fishes and the proteins were analyzed by staining and immunoblotting. All species showed a 36 K protein, two or more glycosylated hydrophobic intermediate protein (IP) components and several myelin basic protein bands (BP). The 36 K protein was specific for teleostean fishes. The IP and BP components displayed substantial variations in their proportions as well as in molecular sizes when comparing the different teleosts. This contrasts with CNS myelin proteins which appear more stable in terrestrial vertebrates.     

Growth properties and biochemical characterization of mouse Schwann cells cultured in vitro

Purified secondary cultures of mouse Schwann cells (less than 5% fibroblast contamination) have been obtained by taking advantage of the differential adhesion of Schwann cells and fibroblasts during trypsinization. The growth properties of the purified subcultures changed with time in culture. Cells passaged after 5 days in vitro (DIV) divided rapidly (doubling time 22 h), whereas cells that had been in vitro for longer periods progressively decreased their growth rate, becoming quiescent after 20 or more days. Schwann cells lacked the Thy 1.2 surface antigen, but were positively stained with antigalactocerebroside antibodies after prefixation. Biochemical analyses showed Schwann cells to be enriched in the activities of enzymes characteristic of the myelin-forming cells: 2′3′-cyclic nucleotide 3′-phosphodiesterase (CNP), cerebroside sulfotransferase (CST) and UDP-galactose: ceramide galactosyltransferase (CGalT).     

Developmental change in a myelin-associated glycoprotein: a comparative study in rodents

In developing rats, a fucose-labeled glycoprotein (mGP) which is closely associated with myelin has a higher apparent molecular weight in immature myelin in comparison with mature myelin. In order to see whether this developmental difference occurred in other species, we investigated different rodents of the suborder Myomorpha. Glycoproteins were labeled in vivo by injection of [³H]fucose of [¹⁴C]fucose, and purified myelin fractions were prepared. Proteins were extracted with SDS and separated by polyacrylamide gel electrophoresis. Using double-labeling techniques, the ³H- and ¹⁴C-labeled mGP were compared in different samples. We found the shift in the apparent molecular weight of mGP during development in rats, gerbils, and hamsters, but we were unable to demonstrate it in mice and prairie deer mice. In these latter species, the mGP of smaller apparent molecular weight was already present at the earliest ages at which it was possible to isolate myelin. Although some rodents do not exhibit the developmental change, all showed a common feature: the presence of the same small molecular weight mGP in mature myelin. It may be that the glycoprotein of smaller size is a prerequisite for the normal compaction and maturation of myelin.