Efficient regulation of nitrogen metabolism likely plays a role in the ability of fungi to exploit ecological niches. To learn about regulation of nitrogen metabolism in the rice blast pathogen Magnaporthe grisea, we undertook a genome-wide analysis of gene expression under nitrogen-limiting conditions. Five hundred and twenty genes showed increased transcript levels at 12 and 48 h after shifting the fungus to media lacking nitrate as a nitrogen source. Thirty-nine of these genes have putative functions in amino acid metabolism and uptake, and include the global nitrogen regulator in M. grisea, NUT1. Evaluation of seven nitrogen starvation-induced genes revealed that all were expressed during rice infection. Targeted gene replacement on one such gene, the vacuolar serine protease, SPM1, resulted in decreased sporulation and appressorial development as well as a greatly attenuated ability to cause disease. Data are discussed in the context of nitrogen metabolism under starvation conditions, as well as conditions potentially encountered during invasive growth in planta.
" pro - duced during infection by phytopathogenic fungi ( Poussereau et al . , 2001 ; ten Have et al . , 2004 ) , their possible role ( s ) in patho - genesis has not been unequivocally established . Targeted gene disruption of the Magnaporthe grisea SPM1 gene , which codes for a vacuolar serine protease , resulted in greatly attenuated virulence ( Donofrio et al . , 2006 ) . However , single and double B . cinerea mutants lacking five different aspartic proteinase encoding genes were as virulent as the parental strain ( ten Have et al . , 2010 ) ."
[Show abstract][Hide abstract] ABSTRACT: The fungus Penicillium digitatum, the causal agent of the green mould rot, is the most destructive postharvest pathogen of citrus fruit in Mediterranean regions. In order to identify P. digitatum genes up-regulated during the infection of oranges that may constitute putative virulence factors, we have followed a PCR-based suppression subtractive hybridization and cDNA macroarray hybridization approach. The origin of ESTs was determined by comparison against the available genome sequences of both organisms. Genes coding for fungal proteases and plant cell wall degrading enzymes represent the largest categories in the subtracted cDNA library. Northern blot analysis of a selection of P. digitatum genes, including those coding for proteases, cell wall related enzymes, redox homoeostasis and detoxification processes, confirmed their up-regulation at varying time points during the infection process. Agrobacterium tumefaciens-mediated transformation was used to generate knockout mutants for two genes encoding a pectin lyase (Pnl1) and a naphthalene dioxygenase (Ndo1). Two independent P. digitatum Δndo1 mutants were as virulent as the wild type. However, the two Δpnl1 mutants analysed were less virulent than the parental strain or an ectopic transformant. Together, these results provide a significant advance in our understanding on the putative determinants of the virulence mechanisms of P. digitatum.
"In addition, Tps1 control of nitrogen metabolism ensures genes for metabolizing alternative sources of nitrogen can be expressed under the nitrogen limiting conditions that might be found in the nutrient poor apoplast if G6P is present, but are not expressed when G6P is absent (Fernandez et al. 2012). This is important because some M. oryzae virulence-associated genes are expressed in axenic cultures under conditions of nitrogen starvation (Donofrio et al. 2006), and at least two of these— SPM1 encoding a serine protease (Donofrio et al. 2006) and PTH11 encoding a plasma membrane protein (DeZwaan et al. 1999)—are under Tps1 control (Fernandez et al. 2012). Fig. 3 Tps1 integrates carbon and nitrogen metabolism. "
[Show abstract][Hide abstract] ABSTRACT: The rice blast fungus Magnaporthe oryzae is a global food security threat due to its destruction of cultivated rice. Of the world's rice harvest, 10-30 % is lost each year to this pathogen, and changing climates are likely to favor its spread into new areas. Insights into how the fungus might be contained could come from the wealth of molecular and cellular studies that have been undertaken in order to shed light on the biological underpinnings of blast disease, aspects of which we review herein. Infection begins when a three-celled spore lands on the surface of a leaf, germinates, and develops the specialized infection structure called the appressorium. The mature appressorium develops a high internal turgor that acts on a thin penetration peg, forcing it through the rice cuticle and into the underlying epidermal cells. Primary then invasive hyphae (IH) elaborate from the peg and grow asymptomatically from one living rice cell to another for the first few days of infection before host cells begin to die and characteristic necrotic lesions form on the surface of the leaf, from which spores are produced to continue the life cycle. To gain new insights into the biology of rice blast disease, we argue that, conceptually, the infection process can be viewed as two discrete phases occurring in markedly different environments and requiring distinct biochemical pathways and morphogenetic regulation: outside the host cell, where the appressorium develops in a nutrient-free environment, and inside the host cell, where filamentous growth occurs in a glucose-rich, nitrogen-poor environment, at least from the perspective of the fungus. Here, we review the physiological and metabolic changes that occur in M. oryzae as it transitions from the surface to the interior of the host, thus enabling us to draw lessons about the strategies that allow M. oryzae cells to thrive in rice cells.
"Only three of the top 55 genes upregulated by nitrogen starvation were also upregulated in IH. Therefore, it appears that expression in response to nitrogen starvation has relevance to the prepenetration phase when the fungus is growing on the plant surface (Soanes et al., 2002; Donofrio et al., 2006, and references therein) but not to early biotrophic invasion stages of growth inside the plant. "
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