Establishment and regulation of polar growth in Streptomyces

Hempel, Antje (2012) Establishment and regulation of polar growth in Streptomyces. Doctoral thesis, University of East Anglia.

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A fundamental question in developmental biology is how cells establish polarity,
and most strikingly how cells grow polarly. From neuronal dendrites and root
hairs to bud emergence and elongation of yeast, broadly conserved pathways
control cell polarity in eukaryotes. In contrast, virtually nothing is known about
the regulatory mechanisms controlling polar cell growth in prokaryotes. In
evolutionary terms, the most ancient form of polar growth is found in the
branching hyphae of the filamentous bacteria Streptomyces, and it is clear that the
essential coiled-coil protein DivIVA, which forms part of a tip-organising, multiprotein
polarisome complex, plays a key role in the control of cell polarity, apical
growth and hyphal branching in Streptomyces coelicolor. I identified and
characterised two regulatory mechanisms, both reminiscent of aspects of cell
polarity control in eukaryotes.
First, I show that the mechanistic basis of branch-site selection during hyphal
growth in Streptomyces is a novel polarisome splitting mechanism, in which the
apical tip polarisome splits to leave behind a small daughter polarisome on the
lateral membrane as the tip grows away. This daughter polarisome gradually
grows in size, and ultimately initiates the outgrowth of a new branch.
Second, I show that the Ser/Thr protein kinase AfsK is part of an apparatus that
controls the polarisome complex at the hyphal tip. Activated AfsK directly
phosphorylates DivIVA and profoundly alters the subcellular localisation of
DivIVA to establish multiple new sites of polar growth. Thereby, AfsK modulates
apical growth and lateral branching during normal growth and cell wall stress. I
suggest that this is part of a stress response that provides Streptomyces with a
mechanism to dismantle the apical growth apparatus at established hyphal tips
that encounter problems with cell wall synthesis (for example through exposure to
an antibiotic or by hitting a physical obstacle in the soil) and instead direct
emergence of new branches elsewhere along the hyphae.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Users 2259 not found.
Date Deposited: 17 Dec 2012 16:22
Last Modified: 03 May 2013 09:55


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