The characterization of plant actin -binding proteins
Abstract
Many plant cellular processes, including division, expansion, development, responses to pathogen attack, and pollen tube germination and growth are dependent upon restructuring of the actin cytoskeleton. In all eukaryotic cells, actin dynamics are thought to be regulated by a plethora of actin-binding proteins that have been placed into several broad classes based upon their effects on actin organization in vitro. Only a small number of actin-binding proteins have been identified from plants, and even fewer have been well characterized. In order to understand how actin organization is controlled in plant cells it is necessary to characterize the effects of plant actin-binding proteins on actin dynamics, as well as to identify other proteins that might affect their function. Therefore, continuing from previous studies in the lab, I have characterized two plant actin-binding proteins (profilin and fimbrin) for the ability to affect actin organization. Profilins from Zea mays and Chlamydomonas reinhardtii primarily sequester monomeric actin, whereas Arabidopsis thaliana fimbrin crosslinks actin filaments and protects them from depolymerization. Findings of significance include: (1) Arabidopsis fimbrin is a bona fide actin-filament crosslinking protein which binds to actin filaments in a calcium-insensitive manner, (2) Arabidopsis fimbrin stabilizes actin filaments protecting them from depolymerization by profilin, (3) the maize profilin family contains two distinct classes whose isoforms differ in sequence identity, expression patterns, and biochemical properties, (4) even though Arabidopsis fimbrin is not regulated by calcium, the maize profilins cause the depolymerization of significantly more actin in the presence of increasing concentrations of calcium, and (5) unlike any other profilin investigated to date, Chlamydomonas profilin inhibits the exchange of adenine nucleotide on actin. Therefore, we speculate that highly organized actin filaments exist in plant cells even in the presence of high concentrations of profilin because they are stabilized by actin-filament binding proteins like fimbrin.
Degree
Ph.D.
Advisors
Staiger, Purdue University.
Subject Area
Cellular biology|Botany
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