Köhli Michael, Galati Virginie, Boudier Kamila, Roberson Robert W, Philippsen Peter
Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.
J Cell Sci. 2008 Dec 1;121(Pt 23):3878-89. doi: 10.1242/jcs.033852. Epub 2008 Nov 4.
We use the fungus Ashbya gossypii to investigate how its polar growth machinery is organized to achieve sustained hyphal growth. In slowly elongating hyphae exocyst, cell polarity and polarisome proteins permanently localize as cortical cap at hyphal tips, thus defining the zone of secretory vesicle fusion. In tenfold faster growing hyphae, this zone is only slightly enlarged demonstrating a capacity of hyphal growth zones to increase rates of vesicle processing to reach higher speeds. Concomitant with this increase, vesicles accumulate as spheroid associated with the tip cortex, indicating that a Spitzenkörper forms in fast hyphae. We also found spheroid-like accumulations for the exocyst components AgSec3, AgSec5, AgExo70 and the polarisome components AgSpa2, AgBni1 and AgPea2 (but not AgBud6 or cell polarity factors such as AgCdc42 or AgBem1). The localization of AgSpa2, AgPea2 and AgBni1 depend on each other but only marginally on AgBud6, as concluded from a set of deletions. Our data define three conditions to achieve fast growth at hyphal tips: permanent presence of the polarity machinery in a confined cortical area, organized accumulation of vesicles and a subset of polarity components close to this area, and spatial separation of the zones of exocytosis (tip front) and endocytosis (tip rim).
我们利用棉阿舒囊霉来研究其极性生长机制是如何组织以实现持续的菌丝生长的。在缓慢伸长的菌丝中，外泌体、细胞极性和极化体蛋白永久定位于菌丝顶端的皮质帽，从而确定分泌囊泡融合的区域。在生长速度快十倍的菌丝中，该区域仅略有扩大，表明菌丝生长区有能力提高囊泡加工速率以达到更高速度。伴随着这种增加，囊泡以与顶端皮质相关的球体形式积累，表明在快速生长的菌丝中形成了一个“尖端复合体”。我们还发现了外泌体成分AgSec3、AgSec5、AgExo70以及极化体成分AgSpa2、AgBni1和AgPea2（但不是AgBud6或细胞极性因子如AgCdc42或AgBem1）的类球体积累。从一组缺失实验得出，AgSpa2、AgPea2和AgBni1的定位相互依赖，但仅略微依赖于AgBud6。我们的数据定义了在菌丝顶端实现快速生长的三个条件：极性机制在受限的皮质区域永久存在、囊泡和靠近该区域的一部分极性成分有组织地积累，以及胞吐作用区域（尖端前端）和胞吞作用区域（尖端边缘）的空间分离。
