A nonpathogenic REMI mutant of Colletotrichum acutatum, designated Ca-5, was isolated whereby in the absence of an external nitrogen source exhibited extended germ tube growth prior to appressoria formation on solid surface and strawberry leaf. Ca-5 exhibited restricted hyphal growth and did not cause lesions on plants but grew necrotrophically when inoculated directly onto wounded sites. The deduced amino acid sequence of the REMI-impaired gene product, designated Nir1, is highly similar to the Aspergillus nidulans NirA protein, a transcriptional regulator of nitrogen metabolism. Inoculation of leaves with wild type or Ca-5 conidia in the presence of a nitrogen source resulted in massive epiphytic hyphal production, appressoria formation and rapid symptom development. The nutritional status of C. acutatum at an early stage of colonization and appressoria formation was assessed by following the expression of nitrate reductase (NR) and glutamine synthetase (GS) in different media. Under all growth conditions there was no effect on GS, however, NR was induced by nitrate and repressed by a rich medium. In addition, NR transcription increased at the appressoria stage, indicating that nitrogen starvation constitutes a cue for regulation of appresoria development. Our results suggest that nitrogen starvation stimulates synchronous preinfection development which is lacking in Ca-5.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)