Abstract
Higher order actin filament structures are necessary for cytoplasmic streaming, organelle movement, and other physiological processes. However, the mechanism by which the higher order cytoskeleton is formed in plants remains unknown. In this study, we identified a novel actin-cross-linking protein family (named CROLIN) that is well conserved only in the plant kingdom. There are six isovariants of CROLIN in the Arabidopsis genome, with CROLIN1 specifically expressed in pollen. In vitro biochemical analyses showed that CROLIN1 is a novel actin-cross-linking protein with binding and stabilizing activities. Remarkably, CROLIN1 can cross-link actin bundles into actin networks. CROLIN1 loss of function induces pollen germination and pollen tube growth hypersensitive to latrunculin B. All of these results demonstrate that CROLIN1 may play an important role in stabilizing and remodeling actin filaments by binding to and cross-linking actin filaments.
Highlights
Higher order actin filament structures are involved in many cellular processes
These results indicate that CROLIN1 may be involved in stabilizing actin structures during pollen germination and pollen tube growth
Over 23 classes of actin-binding proteins (ABPs) that are responsible for regulating the formation of actin structures have been discovered (2)
Summary
Higher order actin filament structures are involved in many cellular processes. Results: Arabidopsis CROLIN1 contains a predicted actin-cross-linking domain and shows F-actin binding, cross-linking, and stabilizing activities in vitro. CROLIN1 loss of function induces pollen germination and pollen tube growth hypersensitive to latrunculin B All of these results demonstrate that CROLIN1 may play an important role in stabilizing and remodeling actin filaments by binding to and cross-linking actin filaments. Arabidopsis actin depolymerization factor 9 (ADF9) facilitates F-actin bundling in vitro (25), and SB401, a pollen-specific protein from Solanum berthaultii, exhibits bundling activity (26) These results imply that plants may have. Pollen tube growth relies on a dynamic and precisely organized actin cytoskeleton (27) During this process, F-actin is maintained as distinct structures and performs specific physiological functions (20, 28, 29). We demonstrate that CROLIN1, a previously undiscovered plant actin-cross-linking protein, is involved in the formation and maintenance of highly ordered actin structures in Arabidopsis
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