Why mushrooms form gills: efficiency of the lamellate morphology

Gilled mushrooms are produced by multiple orders within the Agaricomycetes. Some species form a single array of unbranched radial gills beneath their caps, many others produce multiple files of lamellulae between the primary gills, and branched gills are also common. In this largely theoretical study we modeled the effects of different gill arrangements on the total surface area for spore production. Relative to spore production over a flat surface, gills achieve a maximum 20-fold increase in surface area. The branching of gills produces the same increase in surface area as the formation of free-standing lamellulae (short gills). The addition of lamellulae between every second gill would offer a slightly greater increase in surface area in comparison to the addition of lamellulae between every pair of opposing gills, but this morphology does not appear in nature. Analysis of photographs of mushrooms demonstrates an excellent match between natural gill arrangements and configurations predicted by our model.     

Adaptation of the Spore Discharge Mechanism in the Basidiomycota

Background

Spore discharge in the majority of the 30,000 described species of Basidiomycota is powered by the rapid motion of a fluid droplet, called Buller''s drop, over the spore surface. In basidiomycete yeasts, and phytopathogenic rusts and smuts, spores are discharged directly into the airflow around the fungal colony. Maximum discharge distances of 1–2 mm have been reported for these fungi. In mushroom-forming species, however, spores are propelled over much shorter ranges. In gilled mushrooms, for example, discharge distances of <0.1 mm ensure that spores do not collide with opposing gill surfaces. The way in which the range of the mechanism is controlled has not been studied previously.

Methodology/Principal Findings

In this study, we report high-speed video analysis of spore discharge in selected basidiomycetes ranging from yeasts to wood-decay fungi with poroid fruiting bodies. Analysis of these video data and mathematical modeling show that discharge distance is determined by both spore size and the size of the Buller''s drop. Furthermore, because the size of Buller''s drop is controlled by spore shape, these experiments suggest that seemingly minor changes in spore morphology exert major effects upon discharge distance.

Conclusions/Significance

This biomechanical analysis of spore discharge mechanisms in mushroom-forming fungi and their relatives is the first of its kind and provides a novel view of the incredible variety of spore morphology that has been catalogued by traditional taxonomists for more than 200 years. Rather than representing non-selected variations in micromorphology, the new experiments show that changes in spore architecture have adaptive significance because they control the distance that the spores are shot through air. For this reason, evolutionary modifications to fruiting body architecture, including changes in gill separation and tube diameter in mushrooms, must be tightly linked to alterations in spore morphology.     

Temperature-sensitive gating in a descending visual interneuron, DCMD

Activity in neural circuits can be modified through experience-dependent mechanisms. The effects of high temperature on a locust visual interneuron (the descending contralateral movement detector, DCMD) have previously been shown to be mitigated by prior exposure to sub-lethal, elevated temperatures (heat shock, HS). Activity in the DCMD is reduced at high temperature in naïve animals (control), whereas HS animals show a maintained spike count at all temperatures. We examined whether this finding was due to direct effects of temperature on visual processing, or whether other indirect feedback mechanisms were responsible for the observed effect in the DCMD. Activity in the DCMD was elicited using a computer-generated looming image, and the response was recorded extracellularly. The temperature of visual processing circuits contributes directly to HS-induced plasticity in the DCMD, as maintaining the brain at 25°C during a thoracic temperature ramp eliminated the high frequency activity associated with HS. Removing ascending input by severing the thoracic nerve cord reduced DCMD thermosensitivity, indicating that indirect feedback mechanisms are also involved in controlling the DCMD response to increased thoracic temperature. Understanding how thermosensitive feedback within the locust affects DCMD function provides insight into critical regulatory mechanisms underlying visually-guided behaviors.     

Congenital micropenis: long-term medical, surgical and psychosexual follow-up of individuals raised male or female

OBJECTIVES: To document long-term medical, surgical and psychosexual outcome of individuals with congenital micropenis (13 males, 5 females). METHODS: Physical measurements from childhood were collected retrospectively from medical records and at adulthood by physical examination. An adult psychosexual assessment was conducted with a written questionnaire and oral discussion. RESULTS: Adult penile length was below the normal mean in all men. Three women had vaginoplasty resulting in normal length. All men reported good or fair erections but 50% were dissatisfied with their genitalia. Dissatisfaction with body image resulted from having a small penis (66%), inadequate body hair (50%), gynecomastia (33%) and youthful appearance (33%). Ten men were heterosexual, 1 homosexual and 2 bisexual. Among women, 4 (80%) were dissatisfied with their genitalia. Three women reported average libido with orgasm and were also heterosexual. Two women had no sexual interest or experience. Finally, males were masculine and females feminine in their gender-role identity, and both groups were satisfied with their sex of rearing. CONCLUSIONS: Regarding choice of gender, male sex of rearing can result in satisfactory genito-sexual function. Female gender can also result in success, however it requires extensive feminizing surgery.     

Protein-protein interactions in the complex between the enhancer binding protein NIFA and the sensor NIFL from Azotobacter vinelandii

The enhancer binding protein NIFA and the sensor protein NIFL from Azotobacter vinelandii comprise an atypical two-component regulatory system in which signal transduction occurs via complex formation between the two proteins rather than by the phosphotransfer mechanism, which is characteristic of orthodox systems. The inhibitory activity of NIFL towards NIFA is stimulated by ADP binding to the C-terminal domain of NIFL, which bears significant homology to the histidine protein kinase transmitter domains. Adenosine nucleotides, particularly MgADP, also stimulate complex formation between NIFL and NIFA in vitro, allowing isolation of the complex by cochromatography. Using limited proteolysis of the purified proteins, we show here that changes in protease sensitivity of the Q linker regions of both NIFA and NIFL occurred when the complex was formed in the presence of MgADP. The N-terminal domain of NIFA adjacent to the Q linker was also protected by NIFL. Experiments with truncated versions of NIFA demonstrate that the central domain of NIFA is sufficient to cause protection of the Q linker of NIFL, although in this case, stable protein complexes are not detectable by cochromatography.     

Efficient replication by herpes simplex virus type 1 involves activation of the IkappaB kinase-IkappaB-p65 pathway

Infection by herpes simplex virus type 1 (HSV-1) induces a persistent nuclear translocation of NFkappaB. To identify upstream effectors of NFkappaB and their effect on virus replication, we employed mouse embryo fibroblast (MEF)-derived cell lines with deletions of either IKK1 or IKK2, the catalytic subunits of the IkappaB kinase (IKK) complex. Infected MEFs were assayed for virus yield, loss of IkappaBalpha, nuclear translocation of p65, and NFkappaB DNA-binding activity. Absence of either IKK1 or IKK2 resulted in an 86 to 94% loss of virus yield compared to that of normal MEFs, little or no loss of IkappaBalpha, and greatly reduced NFkappaB nuclear translocation. Consistent with reduced virus yield, accumulation of the late proteins VP16 and gC was severely depressed. Infection of normal MEFs, Hep2, or A549 cells with an adenovirus vector expressing a dominant-negative (DN) IkappaBalpha, followed by superinfection with HSV, resulted in a 98% drop in virus yield. These results indicate that the IKK-IkappaB-p65 pathway activates NFkappaB after virus infection. Analysis of NFkappaB activation and virus replication in control and double-stranded RNA-activated protein kinase-null MEFs indicated that this kinase plays no role in the NFkappaB activation pathway. Finally, in cells where NFkappaB was blocked because of DNIkappaB expression, HSV failed to suppress two markers of apoptosis, cell surface Annexin V staining and PARP cleavage. These results support a model in which activation of NFkappaB promotes efficient replication by HSV, at least in part by suppressing a host innate response to virus infection.     

Biomechanical evidence for convergent evolution of the invasive growth process among fungi and oomycete water molds

Diverse microorganisms traditionally called fungi are recognized as members of two kingdoms: mushroom-forming species and their relatives in the Fungi, and oomycete water molds in the Stramenopila. Phylogenetic analysis suggests that these kingdoms diverged early in the evolution of eukaryotes. The phylogenetic detachment of the fungi and oomycetes is reflected in radical differences in their biochemistry, cell structure, and development. In terms of their biological activities, however, they show great similarity, because both groups form colonies of filamentous hyphae that invade and decompose solid food sources. Here we present biomechanical evidence of the convergent evolution of the invasive growth process in these microorganisms. Using miniature strain gauges to measure the forces exerted by single hyphae, we show that the hyphae of species in both kingdoms exert up to 2 atmospheres of hydrostatic pressure as they extend at their tips. No other eukaryotes have adopted this process for meeting their nutritional needs.     

Two groups control light-induced schiff base deprotonation and the proton affinity of asp(85) in the Arg(82)His mutant of bacteriorhodopsin

Arg(82) is one of the four buried charged residues in the retinal binding pocket of bacteriorhodopsin (bR). Previous studies show that Arg(82) controls the pK(a)s of Asp(85) and the proton release group and is essential for fast light-induced proton release. To further investigate the role of Arg(82) in light-induced proton pumping, we replaced Arg(82) with histidine and studied the resulting pigment and its photochemical properties. The main pK(a) of the purple-to-blue transition (pK(a) of Asp(85)) is unusually low in R82H: 1.0 versus 2.6 in wild type (WT). At pH 3, the pigment is purple and shows light and dark adaptation, but almost no light-induced Schiff base deprotonation (formation of the M intermediate) is observed. As the pH is increased from 3 to 7 the M yield increases with pK(a) 4.5 to a value approximately 40% of that in the WT. A transition with a similar pK(a) is observed in the pH dependence of the rate constant of dark adaptation, k(da). These data can be explained, assuming that some group deprotonates with pK(a) 4.5, causing an increase in the pK(a) of Asp(85) and thus affecting k(da) and the yield of M. As the pH is increased from 7 to 10.5 there is a further 2.5-fold increase in the yield of M and a decrease in its rise time from 200 &mgr;s to 75 &mgr;s with pK(a) 9. 4. The chromophore absorption band undergoes a 4-nm red shift with a similar pK(a). We assume that at high pH, the proton release group deprotonates in the unphotolyzed pigment, causing a transformation of the pigment into a red-shifted "alkaline" form which has a faster rate of light-induced Schiff base deprotonation. The pH dependence of proton release shows that coupling between Asp(85) and the proton release group is weakened in R82H. The pK(a) of the proton release group in M is 7.2 (versus 5.8 in the WT). At pH < 7, most of the proton release occurs during O --> bR transition with tau approximately 45 ms. This transition is slowed in R82H, indicating that Arg(82) is important for the proton transfer from Asp(85) to the proton release group. A model describing the interaction of Asp(85) with two ionizable residues is proposed to describe the pH dependence of light-induced Schiff base deprotonation and proton release.     

Two water molds can grow without measurable turgor pressure

The water molds Achlya bisexualis Coker and Saprolegnia ferax (Gruithuisen) Thuret (Class: Oomycetes) normally grow in the form of slender hyphae with up to 0.8 MPa (8 bar) of internal pressure. Models of plant cell growth indicate that this turgor pressure drives the expansion of the cell wall. However, under conditions of prolonged osmotic stress, these species were able to grow in the absence of measurable turgor. Unpressurized cells of A. bisexualis grew in the form of a plasmodium-like colony on solid media, and produced a multinucleate yeast-like phase in liquid. By contrast, the morphology of S. ferax was unaffected by the loss of turgor, and the mold continued to generate tip-growing hyphae. Measurements of cell wall strength indicate that these microorganisms produce a very fluid wall in the region of surface growth, circumventing the usual requirement for turgor.Abbreviations DAPI 4,6-diamidino-2-phenylindole - PEG polyethylene glycol This work was supported by National Science Foundation grant DCB 90-17130.