Ayad-Durieux Y, Knechtle P, Goff S, Dietrich F, Philippsen P
Department of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
J Cell Sci. 2000 Dec;113 Pt 24:4563-75. doi: 10.1242/jcs.113.24.4563.
Filamentous fungi grow by hyphal extension, which is an extreme example of polarized growth. In contrast to yeast species, where polarized growth of the tip of an emerging bud is temporally limited, filamentous fungi exhibit constitutive polarized growth of the hyphal tip. In many fungi, including Ashbya gossypii, polarized growth is reinforced by a process called hyphal maturation. Hyphal maturation refers to the developmental switch from slow-growing hyphae of young mycelium to fast-growing hyphae of mature mycelium. This process is essential for efficient expansion of mycelium. We report for the first time on the identification and characterization of a fungal gene important for hyphal maturation. This novel A. gossypii gene encodes a presumptive PAK (p21-activated kinase)-like kinase. Its closest homolog is the S. cerevisiae Cla4 protein kinase; the A. gossypii protein is therefore called AgCla4p. Agcla4 deletion strains are no longer able to perform the developmental switch from young to mature hyphae, and GFP (green fluorescent protein)-tagged AgCla4p localizes with much higher frequency in mature hyphal tips than in young hyphal tips. Both results support the importance of AgCla4p in hyphal maturation. AgCla4p is also required for septation, indicated by the inability of Agcla4 deletion strains to properly form actin rings and chitin rings. Despite the requirement of AgCla4p for the development of fast-growing hyphae, AgCla4p is not necessary for actin polarization per se, because tips enriched in cortical patches and hyphae with a fully developed network of actin cables can be seen in Agcla4 deletion strains. The possibility that AgCla4p may be involved in regulatory mechanisms that control the dynamics of the actin patches and/or actin cables is discussed.
丝状真菌通过菌丝延伸生长，这是极性生长的一个极端例子。与酵母不同，酵母中新出芽的芽尖的极性生长在时间上是有限的，而丝状真菌的菌丝尖端表现出组成型极性生长。在许多真菌中，包括棉阿舒囊霉，极性生长通过一个称为菌丝成熟的过程得到加强。菌丝成熟是指从年轻菌丝体生长缓慢的菌丝到成熟菌丝体生长快速的菌丝的发育转变。这个过程对于菌丝体的有效扩展至关重要。我们首次报道了鉴定和表征一个对菌丝成熟重要的真菌基因。这个新的棉阿舒囊霉基因编码一种推测的PAK（p21激活激酶）样激酶。它最接近的同源物是酿酒酵母Cla4蛋白激酶；因此，棉阿舒囊霉的这种蛋白被称为AgCla4p。Agcla4缺失菌株不再能够进行从年轻菌丝到成熟菌丝的发育转变，并且绿色荧光蛋白（GFP）标记的AgCla4p在成熟菌丝尖端的定位频率比在年轻菌丝尖端高得多。这两个结果都支持了AgCla4p在菌丝成熟中的重要性。AgCla4p对于隔膜形成也是必需的，这表现为Agcla4缺失菌株无法正确形成肌动蛋白环和几丁质环。尽管AgCla4p对于快速生长菌丝的发育是必需的，但AgCla4p本身对于肌动蛋白极化并非必需，因为在Agcla4缺失菌株中可以看到富含皮质斑的尖端和具有完全发育的肌动蛋白电缆网络的菌丝。本文还讨论了AgCla4p可能参与控制肌动蛋白斑和/或肌动蛋白电缆动态的调节机制的可能性。
