Analysis of Determinants of Binding and Transcriptional Activation of the Pisatin-Responsive DNA Binding Factor of Nectria haematococca. Jie He. Department of Plant Biology and the Maryland Agriculture Experiment Station, University of Maryland, College Park 20742, U.S.A. Yijun Ruan (1), and David Straney. Department of Plant Biology and the Maryland Agriculture Experiment Station, University of Maryland, College Park 20742, U.S.A. MPMI 9:171-179. Accepted 15 November 1995, Copyright 1996 The American Phytopathological Society.

Pisatin is a fungistatic isoflavonoid produced by garden pea. Field isolates of the ascomycete Nectria haematococca mating population VI (anamorph: Fusarium solani) that are highly virulent on pea have been found to possess the PDA1 gene encoding a pisatin detoxifying activity. Expression of PDA 1 is specifically and highly induced by exposure of mycelia to pisatin. A pisatin-responsive DNA-binding activity has previously been identified with properties suggestive of a transcriptional regulator of PDA1. In this study, the sequence determinants for binding this pisatin-responsive factor (PRF) were localized to a 14-bp region through analysis of sequence alterations that reduced PRF binding. Using a homologous in vitro transcription system, a transcriptional activator of PDAl was shown to be present in mycelial extracts that shared the sequence specificity characteristic of the PRF, indicating function of the DNA-binding protein in transcriptional control. A 70-kDa protein was shown to be a DNA-binding component of PRF by three independent assays for DNA-binding proteins: Southwestern (DNA-protein) blotting, UV-crosslinking, and binding to immobilized DNA. These results characterize a transcriptional activator acting on the PDAl promoter that is responsive to a host-specific compound and provide insight into the regulation of fungal genes in response to plant flavonoids.