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846.
Transformation: a tool for studying fungal pathogens of plants 总被引:18,自引:0,他引:18
Plant diseases caused by plant pathogenic fungi continuously threaten the sustainability of global crop production. An effective
way to study the disease-causing mechanisms of these organisms is to disrupt their genes, in both a targeted and random manner,
so as to isolate mutants exhibiting altered virulence. Although a number of techniques have been employed for such an analysis,
those based on transformation are by far the most commonly used. In filamentous fungi, the introduction of DNA by transformation
typically results in either the heterologous (illegitimate) integration or the homologous integration of the transforming
DNA into the target genome. Homologous integration permits a targeted gene disruption by replacing the wild-type allele on
the genome with a mutant allele on transforming DNA. This process has been widely used to determine the role of newly isolated
fungal genes in pathogenicity. The heterologous integration of transforming DNA causes a random process of gene disruption
(insertional mutagenesis) and has led to the isolation of many fungal mutants defective in pathogenicity. A big advantage
of insertional mutagenesis over the more traditional chemical or radiation mutagenesis procedures is that the mutated gene
is tagged by transforming DNA and can subsequently be cloned using the transforming DNA. The application of various transformation-based
techniques for fungal gene manipulation and how they have increased our understanding and appreciation of some of the most
serious plant pathogenic fungi are discussed.
Received 9 May 2001; received after revision 2 July 2001; accepted 3 July 2001 相似文献
847.
Arnaiz-Villena A Guillén J Ruiz-del-Valle V Lowy E Zamora J Varela P Stefani D Allende LM 《Cellular and molecular life sciences : CMLS》2001,58(8):1159-1166
Mitochondrial cytochrome b (cyt b) from 24 Carduelini species including crossbills, bullfinches, grosbeaks, rosefinches, and other related, but not conclusively classified species, was sequenced. These sequences were also compared with all the available sequences from the genera Carduelis, Serinus, and Passer. Phylogenetic analyses consistently gave the same groups of finches and the calculated divergence times suggest that speciation of the studied species occurred between 14 and 3 million years ago (Miocene-Pliocene), appearing before the Passer, Carduelis, and Serinus genera. Pleistocene glaciations may have been important in sub-speciation. Crossbills are integrated within the genus Carduelis, and within redpolls; the common crossbill shows subspeciation with Loxia japonica in the Pleistocene epoch. Pinicola enucleator groups together with bullfinches and is probably the ancestor of the group. Hawfinch is only distantly related to the studied groups, and might either represent an isolated genus or be related to the New World genus Hesperiphona. The grosbeak genera Eophona and Mycerobas are clearly sister groups, and species belonging to the former might have given rise to Mycerobas species. The isolated (in classification) Uragus sibiricus and Haematospiza sipahi are included within the genus Carpodacus (rosefinches); Carpodacus nipalensis is outside the genus Carpodacus in the molecular analyses and might be an isolated species or related to the genus Montifringilla. 相似文献
848.
Sinnarajah S Dessauer CW Srikumar D Chen J Yuen J Yilma S Dennis JC Morrison EE Vodyanoy V Kehrl JH 《Nature》2001,409(6823):1051-1055
The heterotrimeric G-protein Gs couples cell-surface receptors to the activation of adenylyl cyclases and cyclic AMP production (reviewed in refs 1, 2). RGS proteins, which act as GTPase-activating proteins (GAPs) for the G-protein alpha-subunits alpha(i) and alpha(q), lack such activity for alpha(s) (refs 3-6). But several RGS proteins inhibit cAMP production by Gs-linked receptors. Here we report that RGS2 reduces cAMP production by odorant-stimulated olfactory epithelium membranes, in which the alpha(s) family member alpha(olf) links odorant receptors to adenylyl cyclase activation. Unexpectedly, RGS2 reduces odorant-elicited cAMP production, not by acting on alpha(olf) but by inhibiting the activity of adenylyl cyclase type III, the predominant adenylyl cyclase isoform in olfactory neurons. Furthermore, whole-cell voltage clamp recordings of odorant-stimulated olfactory neurons indicate that endogenous RGS2 negatively regulates odorant-evoked intracellular signalling. These results reveal a mechanism for controlling the activities of adenylyl cyclases, which probably contributes to the ability of olfactory neurons to discriminate odours. 相似文献
849.
Opposing effects of Ets and Id proteins on p16INK4a expression during cellular senescence 总被引:46,自引:0,他引:46
Ohtani N Zebedee Z Huot TJ Stinson JA Sugimoto M Ohashi Y Sharrocks AD Peters G Hara E 《Nature》2001,409(6823):1067-1070
850.
The habitat and nature of early life 总被引:21,自引:0,他引:21
Earth is over 4,500 million years old. Massive bombardment of the planet took place for the first 500-700 million years, and the largest impacts would have been capable of sterilizing the planet. Probably until 4,000 million years ago or later, occasional impacts might have heated the ocean over 100 degrees C. Life on Earth dates from before about 3,800 million years ago, and is likely to have gone through one or more hot-ocean 'bottlenecks'. Only hyperthermophiles (organisms optimally living in water at 80-110 degrees C) would have survived. It is possible that early life diversified near hydrothermal vents, but hypotheses that life first occupied other pre-bottleneck habitats are tenable (including transfer from Mars on ejecta from impacts there). Early hyperthermophile life, probably near hydrothermal systems, may have been non-photosynthetic, and many housekeeping proteins and biochemical processes may have an original hydrothermal heritage. The development of anoxygenic and then oxygenic photosynthesis would have allowed life to escape the hydrothermal setting. By about 3,500 million years ago, most of the principal biochemical pathways that sustain the modern biosphere had evolved, and were global in scope. 相似文献