[]~EVIEWS 23 Pfeifer, G.P. et al. (1990) Proc. Natl Acad. Sci. USA 87, 8252-8256 24 Wolffe, A.P. and Brown, D.D. (1986) Cell 47, 217-227 25 Solomon, M.J. and Varshavsky, A. (1987) Mol. Cell. Biol. 7, 3822-3825 26 Bonne-Andrea, C., Wong, M.L. and Alberts, B.M. (1990) Nature 343, 719-726 27 Adams, R.L.P. (1990) Biochem.J. 265, 309-320 28 Gottesfeld, J. and Bloomer, L.S. (1982) Cell 28, 781-791 29 Holmquist, G.P. (1987) Am.J. Hum. Genet. 40, 151-173 30 Graves, J.A.M. (1987) Trends Genet. 3, 252-256 31 Migeon, B.R. (1990) Genet. Res. 56, 91-98 32 Svaren, J. and Chalkley, R. (1990) Trends Genet. 6, 52-56 33 DePamphilis, M.L. (1988) Cell 52, 635-638 34 Pfeifer, G.P., Tanguay, R.L., Steigerwald, S.D. and Riggs, A.D. (1990) GenesDev. 4, 1277-1287 35 Pfeifer, G.P. and Riggs, A.D. (1991) GenesDev. 5, 1102-1113
g s t i l a g o maydis or corn smut fungus belongs to the Basidiomycetes, a group of fungi that includes the c o m m o n m u s h r o o m and many plant pathogens, such as the smuts and rusts. U. maydis is pathogenic only on corn and its close relative teosinte - it causes stunting and induces the formation of tumors (or galls) in many different parts of the plant. U. maydis is dimorphic (Fig. 1): one of the forms is haploid and unicellular, divides by budding, and is nonpathogenic; the other form is filamentous and dikaryotic and requires the plant for its growth. This filamentous form is pathogenic and arises by fusion of two compatible haploid cells (see below). Dimorphism and m a n y of the steps in the life cycle are under the genetic control of two mating type or incompatibility loci, the a and b loci. Recent studies indicate that the a locus e n c o d e s c o m p o n e n t s of a p h e r o m o n e response p a t h w a y and that the
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36 37 38 39 40 41 42 43 44 45
Lewis, J. and Bird, A. (1991) FEBSLett. 285, 155-159 Wolffe, A.P. (1991)J. CellSci. 99, 201-206 Boyes, J. and Bird, A. (1991) Cell64, 1123-1134 Migeon, B.R., de Beur, S.J. and Axelman, J. (1989) Ex'p. Cell Res. 182, 597-609 Villarreal, L.P. (1991) Microbiol. Rev. 55, 512-542 Zhimulev, I.F., Belyaeva, E.S., Bolshakov, V.N. and Mal'ceva, N.I. (1989) Chromosoma 98, 378-387 Karpen, G.H. and Spradling, A.C. (1990) Cell 63, 97-107 Aparicio, O.M., Billington, B.L. and Gottschling, D.E. (1991) Cell66, 1279-1287 Gmnstein, M. (1990) Trends Genet. 6, 395-400 Selker, E.U. (1990) TrendsBiochem. Sci. 15, 103-107
A.D. RIGGS AND G.P. PFEIFER ARE IN THE DEPARTMENT OF BIOLOGY, BECKMAN RESEARCH INSTITUTE OF THE CITY OF
HoPI~ DUARTF,CA 91010, USA.
Ustilago maydis, the delightful blight FLORA BANUETr Recent studies of the corn smut fungus life cycle and its regulation by two mating type loci and otber genes provide a cornucopia of challenges in cell biology, genetics and protein structure. Thefungus can exist in two states: nonpathogenic and pathogenic. The change from one state to the other is accompanied by a change in morphology (yeast-like to fllamentous) and growth properties (saprophytic to parasitic). b locus e n c o d e s a gene regulatory protein. In addition to these loci, three other genes ( f u z l , f u z 2 and rtfl) have recently b e e n identified that are necessary for
~.
i
F'f'
g s t i l a g o maydis or corn smut fungus belongs to the Basidiomycetes, a group of fungi that includes the c o m m o n m u s h r o o m and many plant pathogens, such as the smuts and rusts. U. maydis is pathogenic only on corn and its close relative teosinte - it causes stunting and induces the formation of tumors (or galls) in many different parts of the plant. U. maydis is dimorphic (Fig. 1): one of the forms is haploid and unicellular, divides by budding, and is nonpathogenic; the other form is filamentous and dikaryotic and requires the plant for its growth. This filamentous form is pathogenic and arises by fusion of two compatible haploid cells (see below). Dimorphism and m a n y of the steps in the life cycle are under the genetic control of two mating type or incompatibility loci, the a and b loci. Recent studies indicate that the a locus e n c o d e s c o m p o n e n t s of a p h e r o m o n e response p a t h w a y and that the
O
•
it
Q
e,
36 37 38 39 40 41 42 43 44 45
Lewis, J. and Bird, A. (1991) FEBSLett. 285, 155-159 Wolffe, A.P. (1991)J. CellSci. 99, 201-206 Boyes, J. and Bird, A. (1991) Cell64, 1123-1134 Migeon, B.R., de Beur, S.J. and Axelman, J. (1989) Ex'p. Cell Res. 182, 597-609 Villarreal, L.P. (1991) Microbiol. Rev. 55, 512-542 Zhimulev, I.F., Belyaeva, E.S., Bolshakov, V.N. and Mal'ceva, N.I. (1989) Chromosoma 98, 378-387 Karpen, G.H. and Spradling, A.C. (1990) Cell 63, 97-107 Aparicio, O.M., Billington, B.L. and Gottschling, D.E. (1991) Cell66, 1279-1287 Gmnstein, M. (1990) Trends Genet. 6, 395-400 Selker, E.U. (1990) TrendsBiochem. Sci. 15, 103-107
A.D. RIGGS AND G.P. PFEIFER ARE IN THE DEPARTMENT OF BIOLOGY, BECKMAN RESEARCH INSTITUTE OF THE CITY OF
HoPI~ DUARTF,CA 91010, USA.
Ustilago maydis, the delightful blight FLORA BANUETr Recent studies of the corn smut fungus life cycle and its regulation by two mating type loci and otber genes provide a cornucopia of challenges in cell biology, genetics and protein structure. Thefungus can exist in two states: nonpathogenic and pathogenic. The change from one state to the other is accompanied by a change in morphology (yeast-like to fllamentous) and growth properties (saprophytic to parasitic). b locus e n c o d e s a gene regulatory protein. In addition to these loci, three other genes ( f u z l , f u z 2 and rtfl) have recently b e e n identified that are necessary for
~.
i
F'f'
