Disease relevance of ACT12

• When the act2-1 mutation was combined with another vegetative actin mutation, act7-1, the resulting double mutant exhibited extensive synergistic phenotypes ranging from developmental lethality to severe dwarfism [1].
• In tobacco leaves the mRNA levels of the constitutively expressed ribosomal protein gene Nt-L25 and the actin genes Nt-ACT9 and At-ACT66 were strongly reduced (to approximately 10%) during heat stress [2].
• The actin cytoskeleton and the microtubule system of the cells, as well as the dynamics of root growth, remain unchanged after short-term application of NR, indicating a relatively low toxicity of this chemical [3].
• Hypersensitivity to actin-targeted drugs is a direct consequence of altered microtubule polymer status, demonstrating that cross-talk between microfilaments and microtubules is critical for regulating anisotropic cell expansion [4].

High impact information on ACT12

• Locally activated ROP2, a Rho-related GTPase from plants, activates RIC4 to promote the assembly of cortical actin microfilaments required for localized outgrowth [5].
• This leads to the disruption of actin cytoskeleton in host cells [6].
• Here we show that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments [7].
• The mutant embryos lack microtubules but not actin filaments [8].
• Although sadly missing several North American participants in the wake of events in Washington and New York, the largely European audience was nevertheless treated to fascinating insights into the many roles of actin polymerization and other processes involved in the establishment and maintenance of cell polarity [9].

Biological context of ACT12

• The distorted trichome morphology mutants provide a simple genetic system in which to study mechanisms of actin-dependent morphogenesis [10].
• Actin filaments comprise an essential cytoskeletal array that organizes the cytoplasm during growth and cell division [10].
• Both actin genes have typical plant actin gene structures, including three small introns interrupting the coding region and an intron within the mRNA leader [11].
• The 5' region from both genes, including the promoter region, TATA box, the sequence for the mRNA leader and its intron, and the first 19 actin codons, was fused to a beta-glucuronidase (GUS) reporter gene [11].
• The Arabidopsis actin proteins have an unusually large number of nonconservative amino acid substitutions, which mapped to the surface of the actin molecule, and should effect protein-protein interactions [12].

Anatomical context of ACT12

• The diverse cellular functions of the actin cytoskeleton are mediated by actin-binding proteins that nucleate, destabilize, and bundle actin filaments [10].
• Actin filaments position the endomembrane system and act as a substrate on which organelle motility occurs [10].
• This model was reinforced by genetic studies in the Drosophila central nervous system and Dictyostelium, where the knockout of certain SCAR-complex components leads to excessive SCAR-mediated actin polymerization [13].
• These motors use microtubules (in the case of kinesines and dyneins) or actin filaments (in the case of myosins) as tracks to transport cargo materials intracellularly [14].
• Peroxisome aggregation depends on actin microfilaments and myosin [15].

Associations of ACT12 with chemical compounds

• Living markers for actin block myosin-dependent motility of plant organelles and auxin [16].
• ABA treatment induced inactivation of AtRac GTPases and disruption of the guard cell actin cytoskeleton [17].
• Type II inositol polyphosphate 5-phosphatases (5PTases) in yeast and animals have been known to regulate the level of phosphoinositides and thereby influence various cellular activities, such as vesicle trafficking and actin organization [18].
• Plasma membrane and intracellular pools of AUX1 are interconnected by actin-dependent constitutive trafficking, which is not sensitive to the vesicle trafficking inhibitor brefeldin A [19].
• Pulse application of low concentrations of the actin-depolymerizing drugs cytochalasin D and latrunculin A broadened growing root hair tips (i.e., they increased the area of cell expansion) [20].

Other interactions of ACT12

• The Arabidopsis thaliana ACT4/ACT12 actin gene subclass is strongly expressed throughout pollen development [11].
• This report shows that the use of live markers for actin visualisation may affect motility of cellular compounds and underlines the general need for critical investigation of actin-related processes in wild-type as well as transgenic plants prior to further interpretation [16].
• We show that alcohol inducible expression of GFP-mTalin in root hairs causes severe defects in actin organization, resulting in either the termination of growth, cell death, and/or changes in cell shape [21].

Analytical, diagnostic and therapeutic context of ACT12

• Both RNA gel blot analysis with 3' gene-specific probes and reverse transcriptase-mediated polymerase chain reactions (RT-PCR) with gene-specific primers detected low levels of ACT4 and ACT12 mRNAs in flowers and very high levels in pollen [11].
• The PCR products were transferred to filters and probed for actin at low stringency [22].
• Furthermore, an immunoprecipitation experiment suggested that AtCAP1 interacted with actin in vivo [23].
• Time-lapse confocal microscopy and fluorescence recovery after photobleaching analyses of the actin cytoskeleton labeled with GFP-fABD2 revealed that lateral-filament migration and sliding of individual actin filaments or bundles are processes that contribute to the dynamic and continually reorganizing nature of the actin scaffold [24].
• The model plant Arabidopsis provides many advantages for genetic dissection of the function of this conserved actin-nucleating machinery, yet the existence of this complex in plants has not been determined [25].

References