Transcription of the avirulence gene Avr9 of the fungal tomato pathogen Cladosporium fulvum is regulated by a GATA-type transcription factor in Aspergillus nidulans.

Abstract

The avirulence gene Avr9 of the fungal tomato pathogen Cladosporium fulvum is highly induced during infection of tomato plants. Expression of the Avr9 gene can also be induced in vitro when cells are grown on synthetic liquid medium containing little or no nitrogen. The Avr9 promoter contains six copies of the sequence TAGATA and six additional copies of the core sequence GATA within 0.4 kb upstream of the translation start site. In the filamentous fungi Aspergillus nidulans and Neurospora crassa, these promoter sequences have been identified as the binding sites for a wide-domain GATA-type regulator (AREA in A. nidulans and NIT2 in N. crassa) involved in nitrogen utilization. Quantification of GUS activity of A. nidulans transformants containing a single copy of the fully active Avr9 promoter-uidA (GUS) reporter gene fusion in different areA backgrounds, following starvation for nitrogen, showed that induction of the Avr9 promoter is regulated similarly in A. nidulans and C. fulvum. This suggests that AREA can regulate the Avr9 promoter and that C. fulvum contains an AREA-like regulator that can bind to these specific sequence motifs. Comparison of the induction profiles of Avr9 and niaD showed that Avr9 expression is independent of NIRA, as is niaD expression upon nitrogen starvation. Studies with Avr9 promoter-uidA fusions in which all or most of these sequences had been deleted, showed that Avr9 promoter activity is dependent on the presence of these specific cis-regulatory elements, suggesting that they do indeed function in transcriptional regulation of the Avr9 gene.