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

甲壳素是β-1，4-乙酰氨基葡萄糖(GlcNAc)的均聚物，是许多丝状真菌的主要细胞壁成分之一。到目前为止，我们已经从尼杜拉曲霉中克隆了5个甲壳素合成酶基因(CHSA-CHSD，CSMA)。为了阐明CHSA-CHSD之间的功能关系，我们构建了这些基因的一些双突变体，并分析了它们的特点。首先，我们用透射电子显微镜详细研究了CHSA CHSC双突变体的细胞壁结构。突变体的细胞壁和隔膜加厚，隔膜中央气孔扩张。这些缺陷并没有在每个单一的突变体中观察到。CHSA-CHSC双突变体在固体微量培养上的细胞壁甲壳素含量均高于各突变体和野生型菌株。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(S)。接下来，我们构建了chsB chsB、chsA chsB和chsC chsB双突变株，并对其进行了鉴定。结果表明，在高渗透压条件下，当ChsB的表达受到抑制时，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.