Relationship between secondary metabolism and fungal development.

Filamentous fungi are unique organisms-rivaled only by actinomycetes and plants-in producing a wide range of natural products called secondary metabolites. These compounds are very diverse in structure and perform functions that are not always known. However, most secondary metabolites are produced after the fungus has completed its initial growth phase and is beginning a stage of development represented by the formation of spores. In this review, we describe secondary metabolites produced by fungi that act as sporogenic factors to influence fungal development, are required for spore viability, or are produced at a time in the life cycle that coincides with development. We describe environmental and genetic factors that can influence the production of secondary metabolites. In the case of the filamentous fungus Aspergillus nidulans, we review the only described work that genetically links the sporulation of this fungus to the production of the mycotoxin sterigmatocystin through a shared G-protein signaling pathway.     

Relationship between Secondary Metabolism and Fungal Development

Filamentous fungi are unique organisms—rivaled only by actinomycetes and plants—in producing a wide range of natural products called secondary metabolites. These compounds are very diverse in structure and perform functions that are not always known. However, most secondary metabolites are produced after the fungus has completed its initial growth phase and is beginning a stage of development represented by the formation of spores. In this review, we describe secondary metabolites produced by fungi that act as sporogenic factors to influence fungal development, are required for spore viability, or are produced at a time in the life cycle that coincides with development. We describe environmental and genetic factors that can influence the production of secondary metabolites. In the case of the filamentous fungus Aspergillus nidulans, we review the only described work that genetically links the sporulation of this fungus to the production of the mycotoxin sterigmatocystin through a shared G-protein signaling pathway.     

Cryophilic fungi to denote fungi in the cryosphere

Fungi are widely distributed in the cryosphere where the habitat is constantly or seasonally covered with snow and/or ice. Fungi normally have different cells in their life cycle; fungal thermal dependence varies according to their life cycle stages and is completely different from that of bacteria. Examples are illustrated to show that the concept of psychrophile by Morita (1975) does not apply to fungi, and we propose a new term “cryophilic fungi” for those that spend a certain life stage or whole life cycle (sexual and/or asexual reproductive stages) in the cryosphere.     

Pneumocystis carinii Delanoë, its Ultrastructure and Ultrastructural Affinities*

SYNOPSIS The fine structure of Pneumocystis carinii Delanoë is described in detail and is compared to the fine structure of protozoa and fungi. Pneumocystis does not have ultrastructural affinities to Protozoa but rather to fungi. Specifically, the process of intracystic body formation in the cyst is similar to the formation of ascospores inside a yeast ascus. The significance of the structural similarity between Pneumocystis and fungi is discussed. It is concluded from the ultrastructural evidence that Pneumocystis may indeed be a yeast or have a yeast-like stage in its life cycle. However, Pneumocystis is not completely similar to any fungus whose ultrastructure has been described so far. Perhaps its particular structure may be an adaptation to the parasitic way of life in mammalian lungs. It should be cultivated in order to be sure of its exact taxonomic position.     

Growth and survival of rumen fungi

The life cycle and growth kinetics of an anaerobic rumen fungus (Neocallimastix R1) in liquid and solid media are described, together with its response to light, temperature and oxygen. These results are discussed in relation to the survival of rumen fungi in saliva and faeces of sheep, and the possible routes for the transfer of anaerobic fungi between ruminants. The thallus and life cycle of Neocallimastix R1 are compared with those of aerobic chytrids.     

Antifungal agents as tools in expermental mycology

Both natural and synthetic substances are conveniently used for studying metabolism, genetic aspects, morphogenesis of cell structures, life cycle and differentiation of fungi.     

Germination of the resting sporangia ofPhysoderma maydis,the causal agent ofPhysoderma disease of maize

Summary The structural and developmental characteristics of the resting sporangium in uniflagellate phycomycetes, together with the type of zoospore, are of high taxonomic value. Among these fungi, however, only a few electron microscopic investigations have been published on this topic, mainly due to technical problems. In the present study ofPhysoderma maydis (Blastocladiales) these problems were overcome as the resting sporangia in this species are formed synchronously, in large numbers, the germination is readily induced and the impermeability of the resting sporangium wall can be circumvented by shaking the prefixed sporangia with glass beads.The germination of the resting sporangia ofP. maydis is described by correlative light and electron microscopic studies and discussed in relation to related investigations on sporogenesis: The germination process starts by a breakdown of large electron-dense accretions found in the resting stage. Simultaneously, the peripheral location of the lipid bodies is lost. The large operculum is pushed open by a protrusion of the inner sporangial wall; an additional wall layer is formed during this process. Synaptonemal complexes are found in the nuclei at this stage, as are nuclear division figures which suggests anEuallomyces type of life cycle for this fungus. Cleavage vesicles, formed from dictyosomes or endoplasmic reticulum, ultimately separate the sporangial content into meiospores. The sequential assembly of organelles into the side body complex is described. Sequestering of the ribosomes into a nuclear cap is interpreted as taking place immediately prior to zoospore discharge.     

培菌白蚁与鸡枞菌研究进展

培菌白蚁起源于非洲,蚁巢内具有复杂的社会分工.培菌白蚁依靠独特的蚁巢结构维持内部稳态和气体循环.菌圃是白蚁培育鸡枞菌的场所.鸡枞菌隶属于担子菌亚门,但其传播方式和生活史具有区别于其它担子菌的特点.鸡枞菌协助白蚁进行植物纤维的消化,白蚁则为鸡枞菌提供合适的生长环境,并控制鸡枞菌的遗传结构.培菌白蚁和鸡枞菌形成紧密的共生关...     

Genetic transformation of filamentous fungi

Many filamentous fungi of all taxa can now be subject to DNA-mediated transformation. Many dominant selectable markers are available and the range available is increasing as new genes are cloned. Transformation is especially valuable in cloning genes defined by mutations with selectable phenotypes and is allowing investigation of many problems in fungi with good genetic systems. Increasingly sophisticated techniques for inactivating genes, targetingin vitro generated mutations to specific loci, and altering gene expression and its regulation are being developed. These approaches are being used to investigate the wealth of basic and applied biological problems available in filamentous fungi.     

Uromyces vankyorum sp. nov. and Uromyces atriplicis, putative vicariant rust species of Patagonian and Australian semi-desert biomes

Uromyces vankyorum (Basidiomycota, Uredinales) growing on Atriplex lampa in the cool Patagonian dwarf shrub semi-desert is described as a new species and a new member of the Argentinean rust mycota. The fungus is morphologically similar to Uromyces atriplicis on Atriplex vesicaria from halophytic shrublands of South Australia. U. atriplicis seems to be derived from U. vankyorum as indicated by its shortened life cycle lacking the urediniospore stage. The species are interpreted as trans-pacific vicariants and represent one of the rare examples for the austral South American-Australasian element among rust fungi. The disjunct distribution of rust fungi between austral South America, Australia and New Zealand is reviewed and discussed. Available data suggest migration of rust fungi along Gondwanan land bridges rather than long-distance dispersal of spores by air currents. Part 198 of the series “Studies in Heterobasidiomycetous Fungi” of the Botanical Institute, University of Tübingen     

冬虫夏草菌和蛹虫草菌的研究现状、问题及展望

冬虫夏草菌和蛹虫草菌是两种最著名的虫草菌。从分类学地位、分布、生活史及有性生殖类型、寄主范围、遗传多样性、分子遗传学和基因组学、生态学、人工栽培及产品开发等方面对冬虫夏草菌和蛹虫草菌的研究现状进行总结,指出了研究中存在的一些问题,并对研究前景进行展望。     

Genetic transformation in Aspergilli: tools of the trade

DNA-mediated transformation is a powerful tool that allows the introduction of specific genetic changes in an organism. Transformation of Aspergilli, acclaimed for their wide use in the industry, has been possible for about two decades now. Several basic and applied problems related to fungal biology have been addressed using this technique. Nonetheless, new markers and strategies for transformation are still being developed for these filamentous fungi. Different methods and markers that are currently available for the transformation of Aspergilli are summarized here. The review also brings out the importance of these transformation systems in analyzing fungal gene function. Aspects of Aspergillus niger transformation are selectively emphasized.     

Biology and biocontrol potential of Ampelomyces mycoparasites, natural antagonists of powdery mildew fungi

Historically, pycnidial fungi belonging to the genus Ampelomyces were among the first mycoparasites to be studied in detail and were also the first fungi used as biocontrol agents of plant parasitic fungi. The interactions between host plants, powdery mildew fungi and Ampelomyces mycoparasites are one of the most evident cases of tritrophic relationships in nature although their study has received little attention in fungal and plant ecology so far. Ampelomyces mycoparasites have now become one of the most advanced in terms of commercial development of a fungal biocontrol agent, although there is still a need for more development work to produce a product with reliability approaching that of conventional chemical treatments. This review summarizes the taxonomy, genetic diversity, life cycle, mode of action, natural occurrence, host range, biocontrol potential, mass production and commercialization of these mycoparasites and compares the biocontrol ability of Ampelomyces with that of other fungal antagonists of powdery mildews.     

Use of zoospore concentrations and life cycle parameters in determining the population of anaerobic fungi in the rumen ecosystem

An indirect approach to quantification of the fibrolytic anaerobic fungi in the rumen is described. A mathematical model of the life cycle of anaerobic fungi, based upon observations of the life histories and growth kinetics of these organisms in vitro and in vivo, is constructed and solved in the steady-state to determine the population of particle-attached (substrate-associated) fungal thalli from the concentration of free-swimming zoospores in rumen liquid. The values obtained are broadly consistent with ruminal observations and with observations on faecal populations, which assume that a significant proportion of fungi leaving the rumen (as cysts or spores) can ultimately be accounted for in the faeces.     

Transgenic strawberry: state of the art for improved traits

Strawberry (Fragaria × ananassa Duch.), a member of the Rosaceae family, is one of the most important fruit crops cultivated worldwide. Strawberry is unique within the Rosaceae because it is a rapidly growing herbaceous perennial with a small genome, short reproductive cycle, and facile vegetative and generative propagation for genetic transformation. For these reasons, strawberry has been recognized as excellent germplasm for genetic and molecular studies for the Rosaceae family. Although traditional breeding methods have achieved steady improvement in agronomic traits, the lack of useful economic characters still remains a major challenge. Genetic transformation has opened a new era for greater creativity in strawberry breeding and germplasm by offering an effective method for creating new varieties that selectively targets a specific interested gene or a few heterologous traits. Enormous advances have been made in strawberry genetic transformation since the first transgenic strawberry plant was obtained in 1990. This paper reviews recent progress in genetic transformation of strawberry on increasing resistance to viruses, fungi, insects, herbicides, stress, and achieving better quality. Problems and prospects for future applications of genetic transformation in strawberry are also discussed.     

Life cycle and morphology of Physarum pusillum (Myxomycetes) on agar culture

Myxomycetes (slime molds) are unique eukaryotic microorganisms with both characteristics of fungi and amoebae. Artificial cultures grown under controlled conditions were used to study the life cycle and morphogenesis. Physarum pusillum was collected from the field. Spores were inoculated and cultured with the hanging drop method. The complete life cycle was observed from spore to spore on agar without adding any solid nutrients or bacteria as food. Life cycle morphological characteristics were described for spore germination, myxamoebae, zygote, plasmodium and sporangia formation.     

The diversity of nuclear cycle in microcyclic rust fungi (Uredinales) and its ecological and evolutionary implications

 Nine types with 11 variations of nuclear cycle and associated metabasidium development were distinguished in microcyclic rust fungi. An additional type was recognized in rust fungi with an expanded life cycle. A significant proportion of rust fungi with a reduced life cycle is assumed to have lost a sexual genetic recombination process, being either apomictic or asexual in reproduction. Most species that retain a sexual process in the microcyclic life cycle seem to have become homothallic. During life cycle evolution by the omission of spore stages, these traits might have had a selective advantage for those species that had less opportunity to encounter a genetically different but sexually compatible mate because of isolated patchy distribution or a short growing season. The findings that different populations of a morphologically identifiable species exhibit two or more distinct patterns of nuclear cycle and different metabasidium development indicate that microcyclic lineages might have evolved independently and repeatedly from a macrocyclic parental species. Those lineages are morphologically the same but would differ from each other in their genetics and biology. Received: July 5, 2002 / Accepted: August 5, 2002 Acknowledgment This work was supported in part by a Grant-in-Aid for Scientific Research (no. 09640744) from the Ministry of Education, Science and Culture (now the Ministry of Education, Culture, Sports, Science and Technology), Japan. Correspondence to:Y. Ono     

The Relative Abundance of Mountain Pine Beetle Fungal Associates Through the Beetle Life Cycle in Pine Trees

The mountain pine beetle (MPB) is a native bark beetle of western North America that attacks pine tree species, particularly lodgepole pine. It is closely associated with the ophiostomatoid ascomycetes Grosmannia clavigera, Leptographium longiclavatum, Ophiostoma montium, and Ceratocystiopsis sp.1, with which it is symbiotically associated. To develop a better understanding of interactions between beetles, fungi, and host trees, we used target-specific DNA primers with qPCR to assess the changes in fungal associate abundance over the stages of the MPB life cycle that occur in galleries under the bark of pine trees. Multivariate analysis of covariance identified statistically significant changes in the relative abundance of the fungi over the life cycle of the MPB. Univariate analysis of covariance identified a statistically significant increase in the abundance of Ceratocystiopsis sp.1 through the beetle life cycle, and pair-wise analysis showed that this increase occurs after the larval stage. In contrast, the abundance of O. montium and Leptographium species (G. clavigera, L. longiclavatum) did not change significantly through the MPB life cycle. From these results, the only fungus showing a significant increase in relative abundance has not been formally described and has been largely ignored by other MPB studies. Although our results were from only one site, in previous studies we have shown that the fungi described were all present in at least ten sites in British Columbia. We suggest that the role of Ceratocystiopsis sp.1 in the MPB system should be explored, particularly its potential as a source of nutrients for teneral adults.