Armadillo repeat-containing kinesin represents the versatile plus-end-directed transporter in Physcomitrella

Area of Science:

• Plant cell biology
• Molecular motors
• Cytoskeletal dynamics

Background:

• Kinesin-1 is essential for anterograde transport in animal cells.
• Plants lack kinesin-1 genes, necessitating identification of an equivalent motor protein.
• The function of plant-specific kinesins in intracellular transport remains largely uncharacterized.

Purpose of the Study:

• To identify and characterize the functional equivalent of conventional kinesin in plants.
• To investigate the role of armadillo repeat-containing kinesin (ARK) in intracellular transport and cell growth.
• To explore the conservation of ARK function across different plant species.

Main Methods:

• Analysis of ARK mutants in the moss Physcomitrium patens.
• Assessment of organelle motility (nuclei, chloroplasts, mitochondria, secretory vesicles) in wild-type and mutant cells.
• Functional assays involving ectopic expression of modified ARK proteins.
• Investigation of cell tip growth phenotypes and localization of actin regulators (RopGEFs).
• Complementation studies using ARK homologues from Arabidopsis thaliana.

Main Results:

• ARK mutants exhibited suppressed anterograde motility of multiple organelles.
• Defects in cell tip growth were observed in ARK mutants, linked to mislocalization of actin regulators like RopGEFs.
• Expression and apical localization of RopGEF3 partially rescued the growth phenotype.
• Mutant phenotypes were partially rescued by Arabidopsis ARK homologues, indicating conserved function.

Conclusions:

• Plant armadillo repeat-containing kinesin (ARK) functions as a versatile anterograde transporter, analogous to kinesin-1 in animals.
• ARK is essential for the transport of diverse cargos and plays a critical role in regulating cell tip growth by influencing actin dynamics.
• ARK's function is conserved across plant species, highlighting its fundamental importance in plant cell biology.