Arabidopsis actin-depolymerizing factors (ADFs) 1 and 9 display antagonist activities

AbstractWe provide evidence that one of the 11 Arabidopsis actin-depolymerizing factors (ADFs), namely ADF9, does not display typical F-actin depolymerizing activity. Instead, ADF9 effectively stabilizes actin filaments in vitro and concomitantly bundles actin filaments with the highest efficiency under acidic conditions. Competition experiments show that ADF9 antagonizes ADF1 activity by reducing its ability to potentiate F-actin depolymerization. Accordingly, ectopic expression of ADF1 and ADF9 in tobacco cells has opposite effects. ADF1 severs actin filaments/bundles and promotes actin cytoskeleton disassembly, whereas ADF9 induces the formation of long bundles. Together these data reveal an additional degree of complexity in the comprehension of the biological functions of the ADF family and illustrate that antagonist activities can be displayed by seemingly equivalent actin-binding proteins

Abscisic acid signal transduction

In dieser Arbeit erfolgte die Charakterisierung eines Schlüsselregulators der Abscisinsäure-Signaltransduktion, der PP2C Phosphatase ABI1, und ihres Interaktionspartners, des Transkriptionsfaktors ATHB6. Über bimolekulare Fluoreszenz-Komplementation wurde die Wechselwirkung zwischen ATHB6 und ABI1 in planta beobachtet. Die funktionelle Analyse eines ABI1-Kernsignals (NLS) zeigte die direkte Abhängigkeit der ABI1-Wirkung von der Funktionalität dieses Motivs: mutierte und deletierte Formen der NLS hoben die durch ABI1 und das punktmutierte abi1-Protein vermittelte ABA-Insensitivität bei der Genexpression in Protoplasten und bei physiologischen Prozessen in transgenen Pflanzen auf. Lokalisationsstudien bei Reporterlinien ergaben eine verstärkte nukleäre Akkumulation von GFP-abi1 gegenüber GFP-ABI1 in Schließzellen und Wurzelzellen. Die präferentielle Akkumulation von GFP-abi1 bildet eine neue Erklärungsbasis für den dominanten ABA-insensitiven abi1-Phänotyp.The plant hormone abscisic acid (ABA) is involved in plant development as well as in adaptation processes to drought, high salt or water stress. The focus of this work lies on the characterisation of the PP2C phosphatase ABI1, a key regulator in ABA signalling, and its interaction partner ATHB6, an HD-Zip transcription factor. The functional analysis of a putative ABI1 nuclear localisation signal (NLS) performed in transiently transformed Arabidopsis protoplasts as well as in stable Arabidopsis overexpressing lines revealed strong dependence on the NLS functionality for the negative regulatory ABI1 function on ABA-dependent promoter activation (RD29B, RAB18) as well as on ABA-regulated physiological processes (germination, root growth or stomata regulation). Studies on subcellular localisation of ABI1 and abi1 reporter fusions display a stronger nuclear accumulation for GFP-abi1 than for GFP-ABI1 in guard cells, epidermal root cells and root meristem cells of 35SS1::GFP-abi1 lines. The preferential nuclear localisation of the mutated PP2C phosphatase might provide a new explanation for the dominant ABA-insensitive phenotype of abi1-plants

Arabidopsis LIM Proteins: A Family of Actin Bundlers with Distinct Expression Patterns and Modes of Regulation[W][OA]

This work systematically examines the expression as well as the actin binding and actin regulatory activities of the Arabidopsis LIM proteins, finding differences in expression and changes in activity, which, for a subset of the LIM proteins, depends on pH and calcium