Banuett F
Department of Biochemistry and Biophysics, University of California San Francisco 94143-0448, USA.
Annu Rev Genet. 1995;29:179-208. doi: 10.1146/annurev.ge.29.120195.001143.
Ustilago maydis induces tumors in maize. It is dimorphic, with a unicellular, nonpathogenic form, and a dikaryotic, filamentous, pathogenic form that requires the plant for its growth. The life cycle is regulated by two mating type loci, a and b: a has two alleles, which encode a pheromone and a receptor; b is multiallelic and encodes a combinatorial homeodomain protein. Cell fusion occurs between haploid cells with different a alleles. The dikaryon formed exhibits filamentous growth if the cells also carry any two different b alleles. The b locus is the major pathogenicity determinant, fuz7, which encodes a MAP kinase activator, is also necessary for tumor induction and may respond to plant signals. Several other genes have been identified (fuz1, fuz2, rtf1, uac, ubc) that affect different aspects of the life cycle transitions. Some of them may identify targets of the b locus. Signaling between pathogen and plant is of key importance in tumor induction and fungal growth and differentiation within the plant. The role of siderophores is also discussed.
玉蜀黍黑粉菌可在玉米中诱发肿瘤。它具有二态性，有单细胞、无致病性的形态，以及双核、丝状、致病的形态，后者需要依赖植物生长。其生命周期受两个交配型基因座a和b调控：a有两个等位基因，编码一种信息素和一种受体；b是多等位基因的，编码一种组合型同源异型域蛋白。细胞融合发生在具有不同a等位基因的单倍体细胞之间。如果细胞还携带任意两个不同的b等位基因，形成的双核体就会呈现丝状生长。b基因座是主要的致病性决定因素，fuz7编码一种丝裂原活化蛋白激酶激活剂，它对于肿瘤诱导也是必需的，并且可能对植物信号作出反应。已经鉴定出其他几个影响生命周期转变不同方面的基因（fuz1、fuz2、rtf1、uac、ubc）。其中一些基因可能确定了b基因座的靶点。病原体与植物之间的信号传导在肿瘤诱导以及真菌在植物体内的生长和分化过程中至关重要。同时也讨论了铁载体的作用。
