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A unique eukaryotic β-xylosidase gene from the phytopathogenic fungus Cochliobolus carbonum

Richard F. Ransom

Department of Energy — Plant Research Laboratory, Michigan State University, East Lansing, Ml 48824, USA

ABSTRACT

The plant-pathogenic fungus Cochliobolus carbonum secretes one major β-xylosidase (Xyp1) when grown on xylan or maize cell walls. cDNA and genomic DNA encoding Xyp1 were isolated using PCR primers based on peptide sequences from the purified protein. XYP1 contains three introns, has 5' and 3' untranslated regions of 74 and 145 bp, respectively, and is predicted to encode a protein of 328 amino acids (M_r 36 700) with four N-glycosylation sites. Although it is secreted, Xyp1 has no predicted signal peptide. Furthermore, Xyp1 appears not to be processed at the N-terminus because one of the peptides isolated from the mature protein is located only six amino acids downstream of the translational start methionine. The primary sequence of Xyp1 is unrelated to any known eukaryotic β-xylosidase but has 35% overall identity to two bacterial bifunctional β-xylosidase/-arabinosidases. Mutation of XYP1 by targeted gene replacement resulted in the loss of the major β-xylosidase activity corresponding to the product of XYP1, but a significant amount of secreted β-xylosidase activity (25% of wild-type) remained in the culture filtrates. The xyp1 mutant was still fully pathogenic on maize.

Author for correspondence: Jonathan D. Walton. Tel: +1 517 353 4885. Fax: +1 517 353 9168. e-mail: walton@pilot.msu.edu

Present address: Department of Pediatric Nephrology, University of Michigan Medical Center, Ann Arbor, Ml 48109, USA.

This article has been cited by other articles:

				N. J. Tonukari, J. S. Scott-Craig, and J. D. Walton The Cochliobolus carbonum SNF1 Gene Is Required for Cell Wall-Degrading Enzyme Expression and Virulence on Maize PLANT CELL, February 1, 2000; 12(2): 237 - 248. [Abstract] [Full Text]