Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Published on May 14, 2008; 10.1104/pp.108.118604

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Received March 2, 2008
Accepted May 8, 2008

An actin binding protein, LlLIM1, mediates Ca and H regulation of actin dynamics in pollen tubes

Huei-Jing Wang , Ai-Ru Wan , and Guang-Yuh Jauh *

Institute of Plant and Microbial Biology, Academia Sinica, Nankang, Taipei, Taiwan, ROC; Institute of Life Science, National Defense Medical Center, Taipei, Taiwan, ROC

* Corresponding author; email: jauh{at}gate.sinica.edu.tw.

Actin microfilaments are crucial for polar-cell tip growth, and their configurations and dynamics are regulated by the actions of various actin-binding proteins (ABPs). We explored the function of a lily (Lilium longiflorum) pollen-enriched LIM-domain-containing protein, LlLIM1, in regulating the actin dynamics in elongating pollen tube. Cytological and biochemical assays verified LlLIM1 functioning as an ABP, promoting F-actin bundle assembly and protecting F-actin against LatB-mediated depolymerization. Overexpressed LlLIM1 significantly disturbed pollen tube growth and morphology, with multiple tubes protruding from one pollen grain and co-aggregation of FM4-64-labeled vesicles and Golgi apparatuses at the subapex of the tube tip. Moderate expression of LlLIM1 induced an oscillatory formation of asterisk-shaped F-actin aggregates that oscillated with growth period but in different phases at the subapical region. These results suggest that the formation of LlLIM1-mediated over-stabilized F-actin bundles interfered with endomembrane trafficking to result in growth retardation. Co-sedimentation assays revealed that the binding affinity of LlLIM1 to F-actin was simultaneously regulated both by pH and Ca2+: LlLIM1 showed a preference for F-actin binding under low pH and low Ca2+ concentration. The potential functions of LlLIM1 as an ABP sensitive to pH and calcium in integrating endomembrane trafficking, oscillatory pH and calcium circumstances to regulate tip-focused pollen tube growth are discussed.






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