Spore morphology of pteridophytes from China Ⅱ. Sinopteridaceae

Spores of 61 species and 6 varieties in 9 genera of the Sinopteridaceae were examined under scanning electron microscope (SEM). Based on surface ornamentation and other features, the spores of the Sinopteridaceae are divided into three types. In type Ⅰ , the exospore is smooth and the surface ornamentation, which is reticulate, cristate, echinate or rugate, is formed by the perispore. All the other genera of this family, except for Onychium and Cryptogramma, have this pattern of spores. In type Ⅱ, the surface ornamentation is formed by both perispore and exospore. This pattern is found only in Cryptogramma. In type Ⅲ, the perispore is thin and the surface ornamentation is formed by the exospore. Onychium is characterized by this type of spores. Those genera with spores of type Ⅰ of the Sinopteridaceae seem to be closely related to each other and should be natural members of this family. The systematic position of Cryptogramma and Onychium, with spores of type Ⅱ and type Ⅲ respectively, however, should be reconsidered. Aleuritopteris might be the mostprimitive member of the Sinopteridaceae from the evidence of spore morph     

Spore Morphology of Pteridophytes from China Ⅵ .Pteridaceae

The spore morphology of 30 species 4 variety of 2 genera of Pteridaceae from China was investigated under scanning electron microscope (SEM) . Among them, 29 species 4 variety belong to the genus Pteris . The spores of Pteris are trilete , radiosymmetrical , subtriangular in polar view and hemispherical or subhemispherical in equatorial view . The polar axes are 26 - 54μm long , and equatorial axes are 34 - 97μm long . The perispore is thin and the surface ornamentation is formed by the exospore . The types of ornamentation are tuberculiform-rugulate , verruciform-rugulate or lophate , the spore of most species with the equatoial flange, some species with proximal ridge and distal ridge . The spore morphology of Pteris is stable, and the difference between species is distinct , but the features of spore and sporophyte are not related. The spore of Histiopteris is monolete and bilaterally symmetrical, elliptical in polar view and kidney-shaped in equatorial view . The polar axes are 22 - 23μm long , and equatorial axes are 29 - 36 μm long . The perispore is thin and the surface ornamentation is formed by the exospore . The surface is rugulate . The spore morphology of Histiopteris and Pteris is very differential , put genus Histiopteris in family Pteridaceae is not suitable, according to the feature of spore morphology .     

Spore morphology of pteridophytes from China Ⅰ. Lygodiaceae

This paper is the first report of an investigation on the spore morphology of Chinese ferns. Spore morphology of 20 species (10 species from China and 10 species from other countries) in the genus Lygodium (Lygodiaceae) was investigated under scanning electron microscope (SEM) and transmission electron microscope (TEM). The spores are tetrahedral-globose, trilete, rarely monolete. The surface ornamentation of the spores can be divided into four main types: In type I , the surface of spores is tuberculate or spheroid-tuberculate. Most of the species of the genus have this type of surface ornamentation of spores. In type II , the surface of spores is smooth. L. palmatum, L . subareolatum , L . yunnanense and L . volubile have this type of surface ornamentation of spores. In type III, both the distal and equatorial areas of spores are coarsely verrucate, while the proximal area is smooth. L. dimorphum, L. digitatum and L. kingii have this type of surface ornamentation of spores. In type IV, the surface of spores is coarsely reticulate. L. scandens and L. reticulatum have this type of surface ornamentation of spores. The surface contours of the reticulate type (type IV) are formed by the exospore, while that of the other types (types I, II, III) are formed by the perispore. The surface ornamentation of spores seems to be stable within species and thus is of important value in the taxonomy of the genus Lygodium.     

Spore morphology of pteridophytes from China Ⅲ. Thelypteridaceae 1. Cyclosorus Link.

Spore morphology of 51 species of Cyclosorus in the Thelypteridaceae from China was investigated using scanning electron microscopy (SEM). The spores are monolete, bilaterosymmetric, ellipsoidal in polar view, and kidney-shaped in equatorial view. On the basis of the variation in their surface ornamentation, the spores fall into three main types. Type I: The surface of spores is echinate or perforate with fimbriate wings. 19 species belong to this type. Type Ⅱ: The surface of spores is cristate. 11 species belong to this type. Type Ⅲ: The surface of spores is echinulate. 10 species belong to this type. The remaining 11 species have spores with mixed surface ornamentation of the above three types, which are considered as intermediate types. The results are valuable for a better understanding of the taxonomy and palynology of the genus Cyclosorus.     

Spore killing in the fungus Podospora anserina: a connection between meiotic drive and vegetative incompatibility?

Fungi in which the haploid nuclei resulting from meiosis are linearly arranged in asci provide unique opportunities to analyse abnormal segregation. Any meiotic drive system in such fungi will be observed in a cross between a driving and a sensitive strain as spore killing: the degeneration of half the ascospores in a certain proportion of the asci. In a sample of some 100 strains isolated from a single natural population we have discovered at least six different meiotic drive elements (van der Gaag et al., 2000). Here we report results of research that was aimed at elucidating a possible correlation between meiotic drive and vegetative incompatibility in eight different Spore killer strains from this population. We show that there is a strong correlation between these two phenotypes, although the precise genetic nature of the correlation is not yet clear. We discuss the implications of our results for the understanding of the population genetics of meiotic drive in Podospora.     

Spore photoproduct within DNA is a surprisingly poor substrate for its designated repair enzyme—The spore photoproduct lyase

DNA repair enzymes typically recognize their substrate lesions with high affinity to ensure efficient lesion repair. In UV irradiated endospores, a special thymine dimer, 5-thyminyl-5,6-dihydrothymine, termed the spore photoproduct (SP), is the dominant DNA photolesion, which is rapidly repaired during spore outgrowth mainly by spore photoproduct lyase (SPL) using an unprecedented protein-harbored radical transfer process. Surprisingly, our in vitro studies using SP-containing short oligonucleotides, pUC 18 plasmid DNA, and E. coli genomic DNA found that they are all poor substrates for SPL in general, exhibiting turnover numbers of 0.01–0.2 min⁻¹. The faster turnover numbers are reached under single turnover conditions, and SPL activity is low with oligonucleotide substrates at higher concentrations. Moreover, SP-containing oligonucleotides do not go past one turnover. In contrast, the dinucleotide SP TpT exhibits a turnover number of 0.3–0.4 min⁻¹, and the reaction may reach up to 10 turnovers. These observations distinguish SPL from other specialized DNA repair enzymes. To the best of our knowledge, SPL represents an unprecedented example of a major DNA repair enzyme that cannot effectively repair its substrate lesion within the normal DNA conformation adopted in growing cells. Factors such as other DNA binding proteins, helicases or an altered DNA conformation may cooperate with SPL to enable efficient SP repair in germinating spores. Therefore, both SP formation and SP repair are likely to be tightly controlled by the unique cellular environment in dormant and outgrowing spore-forming bacteria, and thus SP repair may be extremely slow in non-spore-forming organisms.     

A Recombination Directionality Factor Controls the Cell Type-Specific Activation of σK and the Fidelity of Spore Development in Clostridium difficile

The strict anaerobe Clostridium difficile is the most common cause of nosocomial diarrhea, and the oxygen-resistant spores that it forms have a central role in the infectious cycle. The late stages of sporulation require the mother cell regulatory protein σ^K. In Bacillus subtilis, the onset of σ^K activity requires both excision of a prophage-like element (skin^Bs) inserted in the sigK gene and proteolytical removal of an inhibitory pro-sequence. Importantly, the rearrangement is restricted to the mother cell because the skin^Bs recombinase is produced specifically in this cell. In C. difficile, σ^K lacks a pro-sequence but a skin^Cd element is present. The product of the skin^Cd gene CD1231 shares similarity with large serine recombinases. We show that CD1231 is necessary for sporulation and skin^Cd excision. However, contrary to B. subtilis, expression of CD1231 is observed in vegetative cells and in both sporangial compartments. Nevertheless, we show that skin^Cd excision is under the control of mother cell regulatory proteins σ^E and SpoIIID. We then demonstrate that σ^E and SpoIIID control the expression of the skin^Cd gene CD1234, and that this gene is required for sporulation and skin^Cd excision. CD1231 and CD1234 appear to interact and both proteins are required for skin^Cd excision while only CD1231 is necessary for skin^Cd integration. Thus, CD1234 is a recombination directionality factor that delays and restricts skin^Cd excision to the terminal mother cell. Finally, while the skin^Cd element is not essential for sporulation, deletion of skin^Cd results in premature activity of σ^K and in spores with altered surface layers. Thus, skin^Cd excision is a key element controlling the onset of σ^K activity and the fidelity of spore development.     

Developmentally-Regulated Excision of the SPβ Prophage Reconstitutes a Gene Required for Spore Envelope Maturation in Bacillus subtilis

Temperate phages infect bacteria by injecting their DNA into bacterial cells, where it becomes incorporated into the host genome as a prophage. In the genome of Bacillus subtilis 168, an active prophage, SPβ, is inserted into a polysaccharide synthesis gene, spsM. Here, we show that a rearrangement occurs during sporulation to reconstitute a functional composite spsM gene by precise excision of SPβ from the chromosome. SPβ excision requires a putative site-specific recombinase, SprA, and an accessory protein, SprB. A minimized SPβ, where all the SPβ genes were deleted, except sprA and sprB, retained the SPβ excision activity during sporulation, demonstrating that sprA and sprB are necessary and sufficient for the excision. While expression of sprA was observed during vegetative growth, sprB was induced during sporulation and upon mitomycin C treatment, which triggers the phage lytic cycle. We also demonstrated that overexpression of sprB (but not of sprA) resulted in SPβ prophage excision without triggering the lytic cycle. These results suggest that sprB is the factor that controls the timing of phage excision. Furthermore, we provide evidence that spsM is essential for the addition of polysaccharides to the spore envelope. The presence of polysaccharides on the spore surface renders the spore hydrophilic in water. This property may be beneficial in allowing spores to disperse in natural environments via water flow. A similar rearrangement occurs in Bacillus amyloliquefaciens FZB42, where a SPβ-like element is excised during sporulation to reconstitute a polysaccharide synthesis gene, suggesting that this type of gene rearrangement is common in spore-forming bacteria because it can be spread by phage infection.