The b alleles of U. maydis, whose combinations program pathogenic development, code for polypeptides containing a homeodomain-related motif

Abstract

U. maydis is a fungal pathogen of corn with two forms: one is yeast-like and nonpathogenic; the other is filamentous and pathogenic. The b locus, with 25 different alleles, regulates this dimorphism: any combination of two different alleles triggers pathogenic development, whereas the presence of identical alleles results in the yeast-like form. We have cloned four b alleles (b1, b2, b3, and b4) and show that the b locus contains a single open reading frame (ORF) of 410 amino acids with a variable N-terminal region and a highly conserved C-terminal region (60% and 93% identity, respectively). Mutational analysis confirms that this ORF is responsible for b activity. The b polypeptides appear to be DNA binding proteins because they contain a motif related to the homeodomain in their constant region. We propose that combinatorial interactions between b polypeptides generate regulatory proteins that determine the developmental program of the fungus.

A Secreted Effector Protein ofUstilago maydisGuides Maize Leaf Cells to Form Tumors

“…The isolation of genomic U. maydis DNA was performed as described previously (Schulz et al, 1990). All U. maydis strains (Supplemental Table 4) are derived from SG200 and were generated by insertion of p123 derivatives into the ip locus as described (Loubradou et al, 2001).…”

TheO-Mannosyltransferase PMT4 Is Essential for Normal Appressorium Formation and Penetration inUstilago maydis

“…U. maydis DNA was isolated following the protocol of Hoffman and Winston (1987). Standard U. maydis transformation procedure was used (Schulz et al, 1990). S. pombe molecular genetic techniques were used as described by Moreno et al (1991).…”

Ustilago maydis – a valuable model system for the study of fungal dimorphism and virulence

“…The b gene products belong to the family of homeodomain transcription factors and thus are believed to be either activators or repressors of other specific promoters (Gillissen et al, 1992 ;Schulz et al, 1990). Until recently, all attempts to identify a direct DNA target for the active bW\bE protein complex have been unsuccessful.…”

“…Only if they contain different alleles of the multiallelic b locus is a stable dikaryon formed, which grows as a long straight filament and is able to infect corn plants. The b locus contains a pair of divergently transcribed genes, bW and bE, which both code for putative transcription factors of the homeodomain family (Gillissen et al, 1992 ;Kronstad & Leong, 1990 ;Schulz et al, 1990). The existence of more than 25 different b alleles implies that many hundreds of possible combinations of b alleles, for example, b12 and b22 or b4 and b17, all result in filament formation and pathogenicity .…”