Meyer Vera, Arentshorst Mark, van den Hondel Cees A M J J, Ram Arthur F J
Department of Microbiology and Genetics, Institute of Biotechnology, Berlin University of Technology, Gustav-Meyer-Allee 25, D-13355 Berlin, Germany.
Fungal Genet Biol. 2008 Feb;45(2):152-64. doi: 10.1016/j.fgb.2007.07.006. Epub 2007 Aug 3.
Hyphal tip growth is a key feature of filamentous fungi, however, the molecular mechanism(s) that regulate cell polarity are poorly understood. On the other hand, much more is known about polarised growth in the yeast Saccharomyces cerevisiae. Here, the proteins Spa2p, Bni1p, Bud6p and Pea2p form a protein complex named the polarisome known to be important for the assurance of polar growth. We searched the genome of Aspergillus niger and identified homologues for Spa2p, Bni1p, Bud6p but not for Pea2p. We characterised the function of the Spa2p homologue SpaA by determining its cellular localisation and by constructing deletion and overexpressing mutant strains. SpaA was found to be localised exclusively at the hyphal tip, suggesting that SpaA can be used as marker for polarisation. Deletion and overexpression of spaA resulted in reduced growth rate, increased hyphal diameter and polarity defects, indicating that one of the functions of SpaA is to ensure polarity maintenance. In addition, we could show that SpaA is able to complement the defective haploid invasive growth phenotype of a S. cerevisiae SPA2 null mutant. We suggest that the function of SpaA is to ensure maximal polar growth rate in A. niger.
菌丝顶端生长是丝状真菌的一个关键特征，然而，调节细胞极性的分子机制仍知之甚少。另一方面，对于酿酒酵母中的极性生长了解得更多。在这里，Spa2p、Bni1p、Bud6p和Pea2p蛋白形成了一个名为极化体的蛋白复合物，已知其对确保极性生长很重要。我们搜索了黑曲霉的基因组，鉴定出了Spa2p、Bni1p、Bud6p的同源物，但未鉴定出Pea2p的同源物。我们通过确定其细胞定位以及构建缺失和过表达突变菌株来表征Spa2p同源物SpaA的功能。发现SpaA仅定位于菌丝顶端，这表明SpaA可作为极化的标志物。spaA的缺失和过表达导致生长速率降低、菌丝直径增加和极性缺陷，表明SpaA的功能之一是确保极性维持。此外，我们可以证明SpaA能够弥补酿酒酵母SPA2缺失突变体的缺陷单倍体侵袭生长表型。我们认为SpaA的功能是确保黑曲霉中的最大极性生长速率。
