15th International Conference on Arabidopsis Research - TAIR

T03-043
Cellular localization of AtFH8, an Arabidopsis Class I
formin
Veronika Mikitova(1), Viktor Zarsky(1, 2), Fatima Cvrckova(1)
1- Faculty of Sciences, Charles University, Prague, Czech Republic
2- Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Prague, Czech
Republic
Formins are a family of proteins sharing a core actin-nucleating domain, FH2,
conserved among eukaryotes. Bioinformatic analyses have demonstrated that
formins of higher plants have multiplied and diverged into two classes; one
of them (Class I) consists predominantly of proteins with putative membrane
insertion signals [1,2; see also Poster T06-004]. Membrane association and
role in tip growth have been so far demonstrated by others for a single plant
formin, AtFH1 [3,4].
We have studied the localisation of another Arabidopsis Class I formin,
AtFH8, using GFP-tagged derivatives of this protein, expressed both in a
heterologous transient expression system (Nicotiana benthamiana leaves)
and in stably transformed Arabidopsis, where truncated, C terminally tagged
AtFH8 (AtFH8‘:GFP) has been introduced under the control of the alcoholinducible
promoter, pAlcA. In both cases, we observed cortical localisation,
consistent with plasmalemma association, and occassionally also labelling
of mobile intracellular bodies, either insoluble inclusions or derivatives of
the endomembrane system. However, some nuclear signal was also seen,
corresponding probably to free GFP that was detected on Western blots. In
stable Arabidopsis transformants, we have found that, depending on culture
and induction conditions, the AtFH8‘:GFP mutant protein may interfere with
root hair development, supporting its role in cell morphogenesis.
This work has been supported by GACR204/02/1461 and EU-HPRN-CT-
2002-00265 grants and by a NATO Advanced Fellowship to V. Zarsky. We
thank M. Deeks and P. Hussey for inspiring discussion and methodological
advice.
[1] Genome Biol 1:res 001, 2000 [2] TiPS 7:492, 2002 [3] Plant Cell Physiol 41:617, 2000 [4]
Plant Cell 16:257, 2004
T03 Cell Biology
T03-044
A novel function of cyclin-dependent kinase
inhibitors - KRP1/ICK1 can block mitosis and trigger
endoreduplication
Christina Weinl(1), Suzanne Kuijt(1), Arp Schnittger(1)
1-Unigruppe am Max-Planck-Institut für Züchtungsforschung, Lehrstuhl für Botanik III, Universität
Köln, Carl-von-Linné Weg 10, 50829 Köln, Germany
Control of the cell-division cycle is crucial for organism architecture of all
higher eukaryotes. Cell-cycle progression requires the coordinated activation
and inactivation of a class of serine/threonine protein kinases, called cyclindependent
kinases (CDKs). CDK activity is controlled by various mechanisms
including the binding of phase-specific cyclin partners and phosphorylation/dephosphorylation
at specific sites. An ubiquitously present control
mechanism is the binding of CDK inhibitors (CKIs). In Arabidopsis, a family
of seven low-molecular weight CKIs (KRPs/ICKs) has been identified, which
show homologies to the mammalian p27kip1. Previously, we have shown that
misexpression of KRP1/ICK1 in endoreduplicating trichomes can reduce the
number of endocycles indicating an inhibitory function at the G1/S transition
point in this cellular context.
Here, we show that misexpression of KRP1/ICK1 in dividing cells can
block mitosis but still allows DNA replication leading to enlarged cells with
highly endoreduplicated nuclei. Endoreduplication is often associated with
terminal differentiation; we observed, however, that cell-fate specification
was independent from KRP1/ICK1-induced endoreduplication. Strikingly, we
found that endoreduplicated cells were able to reenter a cell-division program
emphasizing the high degree of flexibility in plant development.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin