1887

Abstract

The impact of mutations affecting microtubule-associated motor proteins on the morphology and cytology of hyphae of was studied. Two mutants, and -, deficient in dynein and dynactin, respectively, were examined by video-enhanced phase-contrast microscopy and image analysis. In contrast to the regular, morphology of wild-type hyphae, the hyphae of the mutants exhibited a great variety of distorted, non-hyphoid morphologies. The hyphae were slow-growing and manifested frequent loss of growth directionality. Cytoplasmic appearance, including organelle distribution and movement, were ostensibly different in the hyphae. The Spitzenkörper (Spk) of wild-type hyphae was readily seen by phase-contrast optics; the Spk of both and was less prominent and sometimes undetectable. Only the fast-growing hyphae displayed a Spk, and it was smaller and less phase-dark than the wild-type Spk. Growth rate in both wild-type and mutants was directly correlated with the size of the Spk. Spk efficiency, measured in terms of cell area generated per Spk travelled distance, was lower in mutants. Another salient difference between mutants and wild-type hyphae was in Spk trajectory. Whereas the Spk of wild-type hyphae maintained a trajectory close to the cell growth axis, the Spk of hyphae moved much more erratically. Sustained departures in the trajectory of the Spk produced corresponding distortions in hyphal morphology. A causal correlation between Spk trajectory and cell shape was tested with the Fungus Simulator program. The characteristic morphologies of wild-type or hyphae were reproduced by the Fungus Simulator, whose vesicle supply centre (VSC) was programmed to follow the corresponding Spk trajectories. This is evidence that the Spk controls hyphal morphology by operating as a VSC. These findings on dynein or dynactin deficiency support the notion that the microtubular cytoskeleton plays a major role in the formation and positioning of the Spk, with dramatic consequences on hyphal growth and morphogenesis.

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2000-07-01
2020-04-04
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