Roles of chitin synthases in hyphal growth and differentiation of filamentous fungi

几丁质是β 1,4 -连接n -乙酰氨基葡萄糖（GlcNAc）的均聚物，是许多丝状真菌细胞壁的主要成分之一。目前，我们已经克隆出5个编码几丁质合成酶的基因（chsA - chsD, csmA）。为了阐明chsA - chsD之间的功能关系，本项目构建了这些基因的双突变体并分析了它们的特征。首先，我们用透射电镜对chsA chsC双突变体细胞壁组织进行了详细的研究。突变体细胞壁和间隔增厚，间隔中心孔扩大。这些缺陷在每个突变体中都没有观察到。chsA chsC双突变体细胞壁的几丁质含量比单突变体和野生型在固体培养基上培养时有所增加。这些结果表明chsA chsC突变引起的细胞壁缺陷激活了其他几丁质合成酶。接下来，我们构建了chsB、chsD、chsA、chsB、chsC、chsB双突变体，并对其进行了结构表征。结果表明，在高渗透压条件下，chsB的表达受到抑制，chsD对菌丝生长的重要性增加，chsA和chsC在菌丝生长中的作用有所不同。

Chitin is a homopolymer of β 1, 4-linked N-acetylglucosamine (GlcNAc) and one of the major cell wall component of many filamentous fungi. We have cloned five genes encoding chitin synthases (chsA - chsD, csmA) from Aspergillus nidulans so far. To elucidate the functional relationships among chsA - chsD, we constructed some sets of double mutants of these genes and analyzed their characteristics in this project. First, we investigate the cell wall organization of chsA chsC double mutant in detail by transmission electron microscopy. The cell walls and septa of the mutant were thickening and central pores of the septa were expanded. These defects were not observed in each single mutant. Chitin content of the cell walls of chsA chsC double mutant increased compared to those of each single mutant and the wild-type strain when they were grown on solid minimal medium. These results suggest that the cell wall defects caused by chsA chsC mutation activated other chitin synthase (s).Next, we constructed chsB chsD, chsA chsB and chsC chsB double mutants and characterized them. The results showed that the importance of chsD increased for hyphal growth under the high osmolarity conditions when the expression of chsB was repressed and that chsA and chsC have some different roles in hyphal growth.