Site-directed mutagenesis of the magB gene affects growth and development in Magnaporthe grisea

Microtubule dynamics during infection-related morphogenesis of Colletotrichum lagenarium

Using a green fluorescent protein (GFP)-tubulin fusion protein, we have investigated the dynamic rearrangement of microtubules during appressorium formation of Colletotrichum lagenarium. Two alpha-tubulin genes of C. lagenarium were isolated, and GFP-alpha-tubulin protein was expressed in this fungus. The strain expressing the fusion protein formed fluorescent filaments that were disrupted by a microtubule-depolymerizing drug, benomyl, demonstrating successful visualization of microtubules. In preincubated conidia, GFP-labeled interphase microtubules, showing random orientation, were observed. At conidial germination, microtubules oriented toward a germination site. At nuclear division, when germ tubes had formed appressoria, mitotic spindles appeared inside conidia followed by disassembly of interphase microtubules. Remarkably, time-lapse views showed that interphase microtubules contact a microtubule-associated center at the cell cortex of conidia that is different from a nuclear spindle pole body (SPB) before their disassembly. Duplicated nuclear SPBs separately moved toward conidium and appressorium accompanied by astral microtubule formation. Benomyl treatment caused movement of both daughter nuclei into 70% of appressoria and affected appressorium morphogenesis. In conidia elongating hyphae without appressoria, microtubules showed polar elongation which is distinct from their random orientation inside appressoria.

Genes expressed during early stages of rice infection with the rice blast fungus Magnaporthe grisea

summary A system-wide approach was adopted to further elucidate mechanisms regulating disease outcome between rice and the fungal pathogen Magnaporthe grisea. First, a cDNA library was constructed from M. grisea infected rice at 48 h post-inoculation. The 5' end-sequencing of 619 randomly selected clones revealed 359 expressed sequence tags (ESTs) that had not previously been described. A total of 124 from 260 ESTs with high and moderate similarity scores, based on BlastX, were organized into categories according to their putative function. The largest category of sequences (21%) contained stress or defence response genes. Eleven per cent of identified ESTs were redundant. In a second approach, differential hybridization analysis of the cDNA library using high-density filters resulted in the identification of novel genes and previously characterized M. grisea genes, including several that had previously been implicated in the infection process. A survey of up-regulated cDNA clones revealed clone 29003, which corresponded to the rice peroxidase POX22.3. This gene is known to be expressed in rice upon infection with Xanthomonas oryzae pv. oryzae, the bacterial blight pathogen. Importantly, this approach demonstrates the utility of gene discovery, through ESTs, for revealing novel genes in addition to those previously characterized as being potentially implicated in host-pathogen interactions.

New (and used) approaches to the study of fungal pathogenicity

The fungi are the most economically important plant pathogens and continue to be the focus of extensive research with a wide variety of methodologies. Enhancements in microscopy techniques have increased our ability to visualize the intimate interaction of fungi and their host plants. Improving methods allow pharmacological inhibition and genetic dissection of the determinants of fungal pathogenicity in a gene-by-gene approach. Identification and analysis of genes differentially transcribed in ways pertinent to pathogenicity continues to be a frequent research approach. Genome-wide analysis is gaining favor in biological research and fungal plant pathogens are no exception. Several industrial research groups are exploring fungal plant pathogenesis based on genomic sequence data and genome-wide mutagenesis. In March 2001 the first publicly available complete genome of a filamentous fungus (Neurospora crassa) was released. N. crassa is of course a saprophyte and there is no complete sequence available for a plant pathogenic fungus in public databases. However, freely accessible entire genome sequences for both plant pathogenic fungi and their hosts are on the horizon. Sequence availability promises to revolutionize the rate at which data relevant to disease processes will be accrued. In this review we describe approaches currently applied to the study of plant pathogenic fungi and explore developments of potential future benefit with existing technologies not yet applied to this group of important organisms.