Schmoll Monika, Schuster André, Silva Roberto do Nascimento, Kubicek Christian P
Research Area Gene Technology and Applied Biochemistry, Institute for Chemical Engineering, Vienna University of Technology, Getreidemarkt 9/1665, Vienna 1060, Austria.
Eukaryot Cell. 2009 Mar;8(3):410-20. doi: 10.1128/EC.00256-08. Epub 2009 Jan 9.
Although the enzymes enabling Hypocrea jecorina (anamorph Trichoderma reesei) to degrade the insoluble substrate cellulose have been investigated in some detail, little is still known about the mechanism by which cellulose signals its presence to the fungus. In order to investigate the possible role of a G-protein/cyclic AMP signaling pathway, the gene encoding GNA3, which belongs to the adenylate cyclase-activating class III of G-alpha subunits, was cloned. gna3 is clustered in tandem with the mitogen-activated protein kinase gene tmk3 and the glycogen phosphorylase gene gph1. The gna3 transcript is upregulated in the presence of light and is almost absent in the dark. A strain bearing a constitutively activated version of GNA3 (gna3QL) exhibits strongly increased cellulase transcription in the presence of the inducer cellulose and in the presence of light, whereas a gna3 antisense strain showed delayed cellulase transcription under this condition. However, the gna3QL mutant strain was unable to form cellulases in the absence of cellulose. The necessity of light for stimulation of cellulase transcription by GNA3 could not be overcome in a mutant which expressed gna3 under control of the constitutive gpd1 promoter also in darkness. We conclude that the previously reported stimulation of cellulase gene transcription by light, but not the direct transmission of the cellulose signal, involves the function and activation of GNA3. The upregulation of gna3 by light is influenced by the light modulator ENVOY, but GNA3 itself has no effect on transcription of the light regulator genes blr1, blr2, and env1. Our data for the first time imply an involvement of a G-alpha subunit in a light-dependent signaling event in fungi.
尽管使嗜热栖热放线菌（无性型里氏木霉）能够降解不溶性底物纤维素的酶已得到一定程度的详细研究，但对于纤维素向真菌发出其存在信号的机制仍知之甚少。为了研究G蛋白/环磷酸腺苷信号通路的可能作用，克隆了编码GNA3的基因，该基因属于Gα亚基的腺苷酸环化酶激活III类。gna3与丝裂原活化蛋白激酶基因tmk3和糖原磷酸化酶基因gph1串联聚集。gna3转录本在有光时上调，在黑暗中几乎不存在。携带组成型激活的GNA3（gna3QL）的菌株在诱导剂纤维素存在和有光的情况下，纤维素酶转录显著增加，而gna3反义菌株在这种条件下纤维素酶转录延迟。然而，gna3QL突变菌株在没有纤维素的情况下无法形成纤维素酶。在一个即使在黑暗中也在组成型gpd1启动子控制下表达gna3的突变体中，光对GNA3刺激纤维素酶转录的必要性无法被克服。我们得出结论，先前报道的光对纤维素酶基因转录的刺激，但不是纤维素信号的直接传递，涉及GNA3的功能和激活。光对gna3的上调受光调节剂ENVOY的影响，但GNA3本身对光调节基因blr1、blr2和env1的转录没有影响。我们的数据首次表明Gα亚基参与了真菌中依赖光的信号事件。
