Lin Xiaorong, Momany Michelle
Department of Plant Biology, University of Georgia, Athens, GA 30602, USA.
Fungal Genet Biol. 2004 Nov;41(11):998-1006. doi: 10.1016/j.fgb.2004.07.005.
Branching generates new axes of polar growth in filamentous fungi and is critical for development, reproduction, and pathogenicity. To investigate branching we screened an Aspergillus nidulans temperature-sensitive mutant collection for abnormal hyphal branch (ahb) mutants. We identified two mutants, ahbA1, which showed reduced branching relative to wild type at restrictive temperature, and ahbB1, which showed increased branching relative to wild type at restrictive temperature. Both mutants also showed abnormal conidiophore development at restrictive temperature. The ahbA1 hypobranching mutant showed defects in nuclear division and hydroxyurea resistance. Complementation and sequencing showed that ahbA1 is a previously identified allele of the cell cycle regulator nimX. The ahbB1 hyperbranching mutant had an increased number of nuclei, was osmotically remedial and Calcofluor resistant. The ahbB gene is predicted to encode a novel protein that has homologues exclusively in filamentous fungi. The C-terminal domain of the predicted AhbB protein showed homology with the heme-binding domain of a cytochrome P450 protein and sequencing of the ahbB1 mutant allele showed that the lesion lies just before this putative heme-binding domain. The ahbB1 mutant showed increased sensitivity to the ergosterol biosynthesis inhibitor imidazole. Our results suggest a link between nuclear division and branching and a possible role for membrane synthesis in branching.
分支在丝状真菌中产生新的极性生长轴，对其发育、繁殖和致病性至关重要。为了研究分支，我们在构巢曲霉温度敏感突变体库中筛选异常菌丝分支（ahb）突变体。我们鉴定出两个突变体，ahbA1，在限制温度下相对于野生型显示分支减少；以及ahbB1，在限制温度下相对于野生型显示分支增加。两个突变体在限制温度下还显示分生孢子梗发育异常。ahbA1低分支突变体在核分裂和羟基脲抗性方面存在缺陷。互补和测序表明ahbA1是细胞周期调节因子nimX先前鉴定的一个等位基因。ahbB1高分支突变体的细胞核数量增加，具有渗透补救性且对荧光增白剂有抗性。预测ahbB基因编码一种仅在丝状真菌中有同源物的新型蛋白质。预测的AhbB蛋白的C末端结构域与细胞色素P450蛋白的血红素结合结构域显示出同源性，并且ahbB1突变等位基因的测序表明损伤恰好位于这个假定的血红素结合结构域之前。ahbB1突变体对麦角固醇生物合成抑制剂咪唑的敏感性增加。我们的结果表明核分裂与分支之间存在联系，并且膜合成在分支中可能发挥作用。
