There are 11 Arabidopsis actin depolymerizing factor (ADF/cofilin) genes in four ancient subclasses that predate the monocot dicot split from a common ancestor. The subclass II ADFs are further divided into two ancient classes (IIa and IIb) in dicots like Arabidopsis. The very specific patterns of class II ADF gene expression are shown here. The other three subclasses are generally expressed in less tissue-specific patterns (Ruzicka et al., 2007)
	Figure Legend.  Analysis of the expression patterns of the four Arabidopsis Subclass II ADF genes. (b-s)  Translational fusions of the subclass II ADF regulatory sequences (p = promoter, 5´UTR, 3´UTR, and polyadenylation signal) with the GUS reporter gene were examined in transgenic Arabidopsis plants.   Histochemical GUS staining was performed on emerging seedling, roots, 7 to 20 day-old plants, and floral organs. (b-f) ADF7p::GUS expression in pollen and pollen tubes (g-k) ADF10p::GUS expression in pollenand pollen tubes (l-o) ADF8p::GUS expression in trichoblast cells and root hairs (p-s) ADF11p::GUS expression in trichoblast cells and root hairs
Summary of the expresson paterns of the four ADF subclasses: Subclass I ADFs (ADF1 to 4)were expressed strongly and constitutively in all vegetative and reproductive tissues except pollen.  Subclass II ADFswere expressed specifically in mature pollen and pollen tubes or root epidermal trichoblast cells and root hairs, and thesepatterns evolved from an ancientdual expression pattern comprised of bothpolar tip-growth cell-types, still observed in the monocot Oryza sativa. Subclass III ADFswere expressed weakly in vegetative tissues, but were strongest in fast growing, and/or differentiating cells including callus, emerging leaves, and meristem regions. The single Subclass IV ADFwas constitutively expressed at moderate levels in all tissues including pollen.  Immunocytochemical analysis with subclass-specific monoclonal antibodies demonstrated that subclass I isovariants (figure below) localize to both the cytoplasm and the nucleus of leaf cells, while subclass II isovariants predominantly localize to the cytoplasm (not shown) at the tip region of elongating root hairs and pollen tubes.  We believe these data on the nuclear localization of some ADF support their role in the nuclear import of actin and indirectly and effect on the epigenetic control of gene expression.

Figure Legend:   Characterization of Subclass I ADFs using Immunolocalization with monoclonal antibody mAbADF4a. (c-h) Immunocytochemical localization of subclass I ADF isovariants with mAbADF4a.  (c) Isolated leaf cell prepared by chemical fixation-method probed with mAbADF4a (d) DAPI (4´,6-diamidino-2-phenylindole) image of DNA in (c) (e) Merge of images shown in (c) and (d) (f, g) Isolated leaf cells prepared by the cryofixation-method probed with mAbADF4a showing localization of ADF protein around chloroplasts and filaments (arrows) (h) Cryofixation-method isolated leaf cell probed with mAbGPa and DAPI showing co-localization of actin (arrows) with mAbADF4a localization in (g)

 

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