KCBP interacts with the cytoskeleton and alters motility in elongating conifer pollen tubes.

Conifer pollen tubes are an interesting model system to study polarized cell growth. Microtubules and microfilaments coordinate to control a unique fountain pattern of organelle streaming within the elongating cell tip. A kinesin like calmodulin binding protein (KCBP) is a unique microtubule motor protein originally discovered in flowering plants that contains two microtubule-binding sites, myosin tail homology, and a regulatory calcium/ calmodulin-binding domain. We are studying KCBP in the conifer pollen tube system of Norway spruce as a potential calcium regulated link between microfilaments and microtubules. We identified a 120 kD KCBP homolog in immunoblots of extracted spruce pollen tube proteins. Using immunofluorescence microscopy, we found that KCBP co localizes with microtubules and microfilaments in the pollen tube tip. We microinjected antibodies that displace calmodulin and activate KCBP into actively growing pollen tubes and found that organelle motility immediately stops after KCBP activation. We propose that activated KCBP induces microtubule reorganization, leading to the cessation of motility. We are currently probing the calcium dependent calmodulin regulation of KCBP by examining cell elongation and organelle motility while perfusing several compounds across elongating pollen tubes that alter calmodulin activity and that alter cytoplasmic calcium levels by affecting cyclic AMP regulation in the cell. This work was supported by the Deparment of Biology and the Office of Undergraduate Research and Creative Activities at the College of Charleston.