Microtubule plus end‐tracking proteins play critical roles in directional growth of hyphae by regulating the dynamics of cytoplasmic microtubules in Aspergillus nidulans

Abstract

SummaryCytoplasmic microtubules (MTs) serve as a ratelimiting factor for hyphal tip growth in the filamentous fungus Aspergillus nidulans. We hypothesized that this function depended on the MT plus end-tracking proteins (+TIPs) including the EB1 family protein EBA that decorated the MT plus ends undergoing polymerization. The ebAΔ mutation reduced colony growth and the mutant hyphae appeared in an undulating pattern instead of exhibiting unidirectional growth in the control. These phenotypes were enhanced by a mutation in another +TIP gene clipA. EBA was required for plus end-tracking of CLIPA, the Kinesin-7 motor KipA, and the XMAP215 homologue AlpA. In addition, cytoplasmic dynein also depended on EBA to track on most polymerizing MT plus ends, but not for its conspicuous appearance at the MT ends near the hyphal apex. The loss of EBA reduced the number of cytoplasmic MTs and prolonged dwelling times for MTs after reaching the hyphal apex. Finally, we found that colonies were formed in the absence of EBA, CLIPA, and NUDA together, suggesting that they were dispensable for fundamental functions of MTs. This study provided a comprehensive delineation of the relationship among different +TIPs and their contributions to MT dynamics and unidirectional hyphal expansion in filamentous fungi.

LIS1 regulates cargo-adapter–mediated activation of dynein by overcoming its autoinhibition in vivo

“…1 D and S2 A). This was not caused by a defect in MT organization, because mCherry-labeled ClipA/Clip170 (Zeng et al, 2014) formed plusend comets in the same cells ( Fig. 1 D).…”

Insights into LIS1 function in cargo-adapter-mediated dynein activation in vivo

“…Upon overexpression of ∆C-HookA, the plusend comets of dynein or dynactin disappeared ( Figure 1D, E, F). This was not caused by a defect in MT organization because mCherry-labelled ClipA/Clip170 (Zeng et al, 2014) formed plus-end comets in the same cells ( Figure 1D). A dominant feature in these cells is the accumulation of dynein and dynactin at septa, which are structures known to contain active microtubule-organizing centers (MTOCs) (Konzack et al, 2005;Xiong and Oakley, 2009;Zekert et al, 2010;Zhang et al, 2017b) (Figure 1E, F).…”

Genetic evidence for a microtubule-capture mechanism during polar growth of Aspergillus nidulans

“…In contrast to KipA (Zeng et al, 2014), for example, MigA still localized to MTs. However, MTs were more uniformly decorated, and MT plus end accumulation was abolished, although this did not completely phenocopy a deletion of the SxIP motif ( Fig.…”

“…In order to test whether MT plus end association of MigA depends on the A. nidulans Eb1 ortholog EbA (Zeng et al, 2014), BiFC assays were performed to determine whether they interact. A strong signal along short and long filamentous structures was observed in hyphae.…”