The ancient subclasses of Arabidopsis ACTIN DEPOLYMERIZING FACTOR genes exhibit novel and differential expression

Abstract

SummaryThe Actin Depolymerizing Factor (ADF) gene family of Arabidopsis thaliana encodes 11 functional protein isovariants in four ancient subclasses. We report the characterization of the tissue-specific and developmental expression of all Arabidopsis ADF genes and the subcellular localization of several protein isovariants. The four subclasses exhibited distinct expression patterns as examined by qRT-PCR and histochemical assays of a GUS reporter gene under the control of individual ADF regulatory sequences. Subclass I ADFs were expressed strongly and constitutively in all vegetative and reproductive tissues except pollen. Subclass II ADFs were expressed specifically in mature pollen and pollen tubes or root epidermal trichoblast cells and root hairs, and these patterns evolved from an ancient dual expression pattern comprised of both polar tip growth cell types, still observed in the monocot Oryza sativa. Subclass III ADFs were 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 ADF was constitutively expressed at moderate levels in all tissues, including pollen. Immunocytochemical analysis with subclass-specific monoclonal antibodies demonstrated that subclass I isovariants localize to both the cytoplasm and the nucleus of leaf cells, while subclass II isovariants predominantly localize to the cytoplasm at the tip region of elongating root hairs and pollen tubes. The distinct expression patterns of the ADF subclasses support a model of ADF s co-evolving with the ancient and divergent actin isovariants.

Nuclear Function of Subclass I Actin-Depolymerizing Factor Contributes to Susceptibility in Arabidopsis to an Adapted Powdery Mildew Fungus

“…S16C). This localization pattern was unexpected, as previous studies reported that ADF4 localized along AFs and throughout the nucleus (Ruzicka et al, 2007;Tian et al, 2009;Daher et al, 2011;Porter et al, 2012). Although T2 plants with GFP fluorescence showed a recovery of powdery mildew susceptibility, in T3 adf4 homozygous plants, the fluorescence intensity was very weak, particularly in mature leaves, and showed little complementation in any of the four isolated lines tested.…”

“…Subclass II is further divided into subclass IIa comprising ADF7 and ADF10, which are specifically expressed in mature pollen grains, and subclass IIb consisting of ADF8 and ADF11, for which expression is limited to the root epidermal cells. ADF5 and ADF9 in subclass III and ADF6 in subclass IV are expressed in a wide variety of tissues (Ruzicka et al, 2007). As in animal cells, ADFs in plants also bind to both monomeric and filamentous actins (Tian et al, 2009;Zheng et al, 2013) and regulate the organization of AFs (Zheng et al, 2013;Henty-Ridilla et al, 2014).…”

“…ADF3 is the most abundantly expressed, approximately 3-fold more than the other three ADFs (Ruzicka et al, 2007). To examine the function of ADFs in the plant-powdery mildew interaction, we inoculated adf1, adf3, and adf4 null mutants with Arabidopsis-adapted G. orontii.…”

“…The organization and dynamics of AFs are regulated by a number of actin-binding proteins, among which actin-depolymerizing factors (ADFs) play a conserved role in actin destabilization by severing and depolymerizing microfilaments at the minus end in eukaryotes, including yeast, mammals, and plants (Maciver and Hussey, 2002;Henty-Ridilla et al, 2013). The Arabidopsis genome contains 11 members of the ADF gene family, which are classified into four subclasses (Ruzicka et al, 2007). Subclass I, which contains ADF1 to ADF4, is expressed at a relatively high level throughout the plant.…”

BABY BOOM target genes provide diverse entry points into cell proliferation and cell growth pathways

“…Recently Ruzicka et al (2007) characterized the expression patterns of the 11 Arabidopsis ADF gene family members using qRT-PCR and GUS reporter gene fusions. They show that ADF9 is expressed at low levels in a broad range of tissues during plant development, and within these tissues shows the strongest expression in rapidly dividing and/or growing cells, such as those of the root and shoot meristem, leaf margins, emerging leaves and root elongation zone.…”