Planar polarity, the polar orientation of cells within the plane of a tissue layer, is intensively studied in animals, but little is known about planar epidermal polarity in plants. We study polar root hair positioning close to distal ends of hair-forming cells (trichoblasts) in the Arabidopsis root epidermis. We have isolated the recessive beatnik (btk) mutant that displays root-specific phenotypes such as long hairs and hyperpolarized hair initiation at distal-most ends of trichoblasts. Map-based cloning, sequencing and complementation of btk revealed that the phenotypes are caused by a novel mis-sense mutation in the protein kinase domain of CONSTITUTIVE TRIPLE RESPONSE1 (CTR1), a RAF kinase acting as a negative regulator of ethylene signalling. Unlike other ctr1 alleles, btk does not display a constitutive triple response thus representing a unique CTR1 allele. Immuno-localization of ROP (RHO-of-plant) small GTPases in btk showed premature hyperpolarized localization to hair initiation sites prior to cell elongation. These findings suggest that CTR1 acts upstream of polar ROP positioning and couples planar polarity to cell elongation.
We propose to analyse the molecular basis of the btk phenotype by determining in vivo protein kinase activity, stability and changes in sub-cellular localization of epitope-tagged CTR1 wild type and btk mutant proteins. Genetic analyses combining btk and other planar polarity mutants (aux1, ein2, act2 etc.) will be employed to place CTR1 action into a signalling cascade. Cre/Lox based mosaic analysis of ctr1-1 and btk loss-of-function and CTR1 over-expression clones should answer where CTR1 modulates planar polarity and whether this involves cell autonomous action. These studies will be extended to btk mosaic analysis in aux1 and e in2 mutants. Analysis of ROP2 fused to photoswitchable cyan fluorescent protein in btk combined with photo-conversion methods should clarify the mechanism by which CTR1 modulates polar ROP relocation.
Field of science
- /natural sciences/biological sciences/biochemistry/biomolecules/proteins
- /natural sciences/chemical sciences/organic chemistry/aliphatic compounds
- /natural sciences/biological sciences/cell biology/cell polarity
- /natural sciences/biological sciences/genetics and heredity/mutation
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