Andrews D L, Egan J D, Mayorga M E, Gold S E
Department of Plant Pathology, University of Georgia, Athens 30602, USA.
Mol Plant Microbe Interact. 2000 Jul;13(7):781-6. doi: 10.1094/MPMI.2000.13.7.781.
Ustilago maydis, the causal agent of corn smut disease, displays dimorphic growth in which it alternates between a budding haploid saprophyte and a filamentous dikaryotic pathogen. We are interested in identifying the genetic determinants of filamentous growth and pathogenicity in U. maydis. To do this we have taken a forward genetic approach. Earlier, we showed that haploid adenylate cyclase (uac1) mutants display a constitutively filamentous phenotype. Mutagenesis of a uac1 disruption strain allowed the isolation of a large number of budding suppressor mutants. These mutants are named ubc, for Ustilago bypass of cyclase, as they no longer require the production of cyclic AMP (cAMP) to grow in the budding morphology. Complementation of a subset of these suppressor mutants led to the identification of the ubc4 and ubc5 genes, which are required for filamentous growth and encode a MAP (mitogen-activated protein) kinase kinase kinase and a MAP kinase kinase, respectively. Evidence suggests that they are important in the pheromone response pathway and in pathogenicity. These results further support an important interplay of the cAMP and MAP kinase signal transduction pathways in the control of morphogenesis and pathogenicity in U. maydis.
玉蜀黍黑粉菌是玉米黑粉病的病原体，表现出双态生长，即在出芽单倍体腐生菌和丝状双核病原体之间交替。我们对鉴定玉蜀黍黑粉菌中丝状生长和致病性的遗传决定因素感兴趣。为此，我们采用了正向遗传学方法。早些时候，我们表明单倍体腺苷酸环化酶（uac1）突变体表现出组成型丝状表型。对uac1缺失菌株进行诱变，使得能够分离出大量出芽抑制突变体。这些突变体被命名为ubc，即玉蜀黍黑粉菌环化酶旁路，因为它们不再需要产生环磷酸腺苷（cAMP）来以出芽形态生长。对这些抑制突变体的一个子集进行互补分析，导致鉴定出ubc4和ubc5基因，它们是丝状生长所必需的，分别编码一种丝裂原活化蛋白（MAP）激酶激酶激酶和一种MAP激酶激酶。有证据表明它们在信息素反应途径和致病性中很重要。这些结果进一步支持了cAMP和MAP激酶信号转导途径在控制玉蜀黍黑粉菌形态发生和致病性方面的重要相互作用。
