Search

Fusarium graminearumis the causal agent of the Fusarium head blight (FHB) and a destructive pathogen of cereals accounting for high grain yield losses especially on wheat and maize. Like other fungal pathogens,F. graminearumsecretes various extracellular enzymes, which are hypothesized to be involved in host infection. Extracellular lipolytic activity ofF. graminearumwas strongly induced in culture by wheat germ oil; this allowed us to isolate, clone, and characterize a gene (FGL1) encoding a secreted lipase. Expression analysis indicated thatFGL1is induced by lipid-containing substrates and repressed by glucose.In planta,FGL1transcription was detected 1 day post-infection of wheat spikes. The function of theFGL1gene product was verified by specifically demonstrating lipase activity after expression in a heterologous host. Ebelactone B, a known lipase inhibitor, repressed the lipolytic activity of the enzyme. Disease severity was strongly reduced when wild-type conidia were supplemented with ebelactone B. Transformation-mediated disruption ofFGL1led to reduced extracellular lipolytic activity in culture and to reduced virulence to both wheat and maize. [ABSTRACT FROM AUTHOR]

Summary During meiosis, homologous recombination occurs between allelic sequences. To evaluate the biological significance of such a pathway in somatic cells, we used transgenic tobacco plants with a restriction site for the rare cutting endonuclease I-Sce I within a negative selectable marker gene. These plants were crossed with two tobacco lines containing, in allelic position, either a deletion or an insertion within the marker gene that rendered both marker gene and restriction site inactive. After the double-strand break induction, we selected for repair events resulting in a loss of marker gene function. This loss was mostly due to deletions. We were also able to detect double strand break-induced allelic recombination in which the break was repaired by a faithful copying process from the homologue carrying the shortened transgene. The estimated frequency indicates that homologous recombination in somatic cells between allelic sites appears to occur at the same order of magnitude as between ectopic sites, and is thus far too infrequent to act as major repair pathway. As somatic changes can be transferred to the germ line, the prevalence of intrachromatid rearrangements over allelic recombination might be an indirect prerequisite for the enhanced genome plasticity postulated for plants. [ABSTRACT FROM AUTHOR]