Transcriptome profiling of the rice blast fungus during invasive plant infection and in vitro stresses

<p>Abstract</p> <p>Background</p> <p>Rice blast is the most threatening disease to cultivated rice. <it>Magnaporthe oryzae</it>, its causal agent, is likely to encounter environmental challenges during invasive growth in its host plants that require shifts in gene expression to establish a compatible interaction. Here, we tested the hypothesis that gene expression patterns during <it>in planta </it>invasive growth are similar to <it>in vitro </it>stress conditions, such as nutrient limitation, temperature up shift and oxidative stress, and determined which condition most closely mimicked that of <it>in planta </it>invasive growth. Gene expression data were collected from these <it>in vitro </it>experiments and compared to fungal gene expression during the invasive growth phase at 72 hours post-inoculation in compatible interactions on two grass hosts, rice and barley.</p> <p>Results</p> <p>We identified 4,973 genes that were differentially expressed in at least one of the <it>in planta </it>and <it>in vitro </it>stress conditions when compared to fungal mycelia grown in complete medium, which was used as reference. From those genes, 1,909 showed similar expression patterns between at least one of the <it>in vitro </it>stresses and rice and/or barley. Hierarchical clustering of these 1,909 genes showed three major clusters in which <it>in planta </it>conditions closely grouped with the nutrient starvation conditions. Out of these 1,909 genes, 55 genes and 129 genes were induced and repressed in all treatments, respectively. Functional categorization of the 55 induced genes revealed that most were either related to carbon metabolism, membrane proteins, or were involved in oxidoreduction reactions. The 129 repressed genes showed putative roles in vesicle trafficking, signal transduction, nitrogen metabolism, or molecular transport.</p> <p>Conclusions</p> <p>These findings suggest that <it>M. oryzae </it>is likely primarily coping with nutrient-limited environments at the invasive growth stage 72 hours post-inoculation, and not with oxidative or temperature stresses.</p

Ochratoxin A and related mycotoxins

Ochratoxins are toxins produced by fungal species belonging not only to Aspergilli but also to Penicillia with ochratoxin A (OTA) being the main toxin of the group followed by ochratoxin B (OTB) and ochratoxin C (OTC). These mycotoxins can occurare formed in a variety of plant products as well as in some animal-derived products following fungal invasion. Human exposure to OTA is mainly due to contaminated cereal products, coffee and red wine. OTA it is continuously studied for its occurrence in different foods and feeds and for its harmfulness for human and animal health. OTA is immunotoxic, nephrotoxic and potentially carcinogenic in animals. Kidneys are its target organs and its level in foods is strictly regulated by laws with OTA being classified as a member of group 2B of carcinogens. According to the molecular structure, several enzymatic activities in addition to the primary pathway for phenylalanine biosynthesis are required for the biosynthesis of ochratoxin A: these are a polyketide synthase for the synthesis of the polyketide dihydroisocoumarin, a chlorinating enzyme, a methylase, an esterase, and a peptide synthetase for ligation of the phenylalanine to the dihydroisocoumarin