Fujioka Tomonori, Mizutani Osamu, Furukawa Kentaro, Sato Natsuko, Yoshimi Akira, Yamagata Youhei, Nakajima Tasuku, Abe Keietsu
Laboratory of Enzymology, Department of Molecular and Cell Biology, Graduate School of Agricultural Science, Tohoku University, 1-1 Amamiya, Tsutsumi-dori, Sendai 981-8555, Japan.
Eukaryot Cell. 2007 Aug;6(8):1497-510. doi: 10.1128/EC.00281-06. Epub 2007 Jun 29.
Cell wall integrity signaling (CWIS) maintains cell wall biogenesis in fungi, but only a few transcription factors (TFs) and target genes downstream of the CWIS cascade in filamentous fungi are known. Because a mitogen-activated protein kinase (MpkA) is a key CWIS enzyme, the transcriptional regulation of mpkA and of cell wall-related genes (CWGs) is important in cell wall biogenesis. We cloned Aspergillus nidulans mpkA; rlmA, a TF gene orthologous to Saccharomyces cerevisiae RLM1 that encodes Rlm1p, a major Mpk1p-dependent TF that regulates the transcription of MPK1 besides that of CWGs; and Answi4 and Answi6, homologous to S. cerevisiae SWI4 and SWI6, encoding the Mpk1p-activating TF complex Swi4p-Swi6p, which regulates CWG transcription in a cell cycle-dependent manner. A. nidulans rlmA and mpkA cDNA functionally complemented S. cerevisiae rlm1Delta and mpk1Delta mutants, respectively, but Answi4 and Answi6 cDNA did not complement swi4Delta and swi6Delta mutants. We constructed A. nidulans rlmA, Answi4 and Answi6, and mpkA disruptants (rlmADelta, Answi4Delta Answi6Delta, and mpkADelta strains) and analyzed mpkA and CWG transcripts after treatment with a beta-1,3-glucan synthase inhibitor (micafungin) that could activate MpkA via CWIS. Levels of mpkA transcripts in the mutants as well as those in the wild type were changed after micafungin treatment. The beta-glucuronidase reporter gene controlled by the mpkA promoter was expressed in the wild type but not in the mpkADelta strain. Thus, mpkA transcription seems to be autoregulated by CWIS via MpkA but not by RlmA or AnSwi4-AnSwi6. The transcription of most CWGs except alpha-1,3-glucan synthase genes (agsA and agsB) was independent of RlmA and AnSwi4-AnSwi6 and seemed to be regulated by non-MpkA signaling. The transcriptional regulation of mpkA and of CWGs via CWIS in A. nidulans differs significantly from that in S. cerevisiae.
细胞壁完整性信号传导（CWIS）维持真菌中的细胞壁生物合成，但丝状真菌中CWIS级联下游只有少数转录因子（TFs）和靶基因是已知的。由于丝裂原活化蛋白激酶（MpkA）是一种关键的CWIS酶，因此mpkA和细胞壁相关基因（CWGs）的转录调控在细胞壁生物合成中很重要。我们克隆了构巢曲霉的mpkA；rlmA，它是酿酒酵母RLM1的直系同源TF基因，编码Rlm1p，Rlm1p是一种主要的Mpk1p依赖性TF，除了调节CWGs的转录外，还调节MPK1的转录；以及Answi4和Answi6，它们与酿酒酵母的SWI4和SWI6同源，编码Mpk1p激活TF复合物Swi4p-Swi6p，该复合物以细胞周期依赖性方式调节CWG转录。构巢曲霉的rlmA和mpkA cDNA分别在功能上互补酿酒酵母的rlm1Δ和mpk1Δ突变体，但Answi4和Answi6 cDNA不能互补swi4Δ和swi6Δ突变体。我们构建了构巢曲霉的rlmA、Answi4和Answi6以及mpkA缺失突变体（rlmAΔ、Answi4ΔAnswi6Δ和mpkAΔ菌株），并用β-1,3-葡聚糖合酶抑制剂（米卡芬净）处理后分析mpkA和CWG转录本，该抑制剂可通过CWIS激活MpkA。米卡芬净处理后，突变体以及野生型中的mpkA转录本水平均发生了变化。由mpkA启动子控制的β-葡萄糖醛酸酶报告基因在野生型中表达，但在mpkAΔ菌株中不表达。因此，mpkA转录似乎由CWIS通过MpkA进行自调控，而不是由RlmA或AnSwi4-AnSwi6调控。除α-1,3-葡聚糖合酶基因（agsA和agsB）外，大多数CWGs的转录独立于RlmA和AnSwi4-AnSwi6，似乎受非MpkA信号传导调控。构巢曲霉中通过CWIS对mpkA和CWGs的转录调控与酿酒酵母中的显著不同。
