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The SH3/PH Domain Protein AgBoi1/2 Collaborates with the Rho-Type GTPaseAgRho3 To Prevent Nonpolar Growth at Hyphal Tips of Ashbyagossypii
Unlike most other cells, hyphae of filamentous fungi permanently elongate and lack nonpolar growth phases. We identified AgBoi1/2p in the filamentous ascomycete Ashbya gossypii as a component required to prevent nonpolar growth at hyphal tips. Strains lacking AgBoi1/2p frequently show spherical enla...
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Published in: | Eukaryotic cell 2006-10, Vol.5 (10), p.1635-1647 |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Unlike most other cells, hyphae of filamentous fungi permanently elongate and
lack nonpolar growth phases. We identified AgBoi1/2p in the filamentous
ascomycete
Ashbya gossypii
as a component required to prevent
nonpolar growth at hyphal tips. Strains lacking AgBoi1/2p frequently
show spherical enlargement at hyphal tips with concomitant
depolarization of actin patches and loss of tip-located actin cables.
These enlarged tips can repolarize and resume hyphal tip extension in
the previous polarity axis. AgBoi1/2p permanently localizes to hyphal
tips and transiently to sites of septation. Only the tip localization
is important for sustained elongation of hyphae. In a yeast two-hybrid
experiment, we identified the Rho-type GTPase AgRho3p as an interactor
of AgBoi1/2p. AgRho3p is also required to prevent nonpolar growth at
hyphal tips, and strains deleted for both Ag
BOI1/2
and Ag
RHO3
phenocopied the respective
single-deletion strains, demonstrating that AgBoi1/2p and AgRho3p
function in a common pathway. Monitoring the polarisome of growing
hyphae using AgSpa2p fused to the green fluorescent protein as a
marker, we found that polarisome disassembly precedes the onset of
nonpolar growth in strains lacking AgBoi1/2p or AgRho3p. AgRho3p locked
in its GTP-bound form interacts with the Rho-binding domain of the
polarisome-associated formin AgBni1p, implying that AgRho3p has the
capacity to directly activate formin-driven actin cable nucleation. We
conclude that AgBoi1/2p and AgRho3p support polarisome-mediated actin
cable formation at hyphal tips, thereby ensuring permanent polar tip
growth. |
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ISSN: | 1535-9778 1535-9786 |
DOI: | 10.1128/EC.00210-06 |