Abstract
Using genetic approaches, particle image velocimetry and an inert tracer of cytoplasmic streaming, we have made a mechanistic connection between the motor proteins (myosins XI), cargo transported by these motors (distinct endomembrane compartment defined by membrane-anchored MyoB receptors) and the process of cytoplasmic streaming in plant cells. It is shown that the MyoB compartment in Nicotiana benthamiana is highly dynamic moving with the mean velocity of ~3 μm/sec. In contrast, Golgi, mitochondria, peroxisomes, carrier vesicles and a cytosol flow tracer share distinct velocity profile with mean velocities of 0.6–1.5 μm/sec. Dominant negative inhibition of the myosins XI or MyoB receptors using overexpression of the N. benthamiana myosin cargo-binding domain or MyoB myosin-binding domain, respectively, resulted in velocity reduction for not only the MyoB compartment, but also each of the tested organelles, vesicles and cytoplasmic streaming. Furthermore, the extents of this reduction were similar for each of these compartments suggesting that MyoB compartment plays primary role in cytosol dynamics. Using gene knockout analysis in Arabidopsis thaliana, it is demonstrated that inactivation of MyoB1-4 results in reduced velocity of mitochondria implying slower cytoplasmic streaming. It is also shown that myosins XI and MyoB receptors genetically interact to contribute to cell expansion, plant growth, morphogenesis and proper onset of flowering. These results support a model according to which myosin-dependent, MyoB receptor-mediated transport of a specialized membrane compartment that is conserved in all land plants drives cytoplasmic streaming that carries organelles and vesicles and facilitates cell growth and plant development.
Highlights
How molecules and large macromolecular complexes are properly distributed and positioned is one of the central problems of cell biology
To take advantage of a facile transient gene expression system in Nicotiana benthamiana, we isolated genomic clones of the N. benthamiana MyoB1 and MyoB2 orthologs of Arabidopsis MyoB1 and MyoB2, tagged each of them by inserting the GFP ORF, and found that the resulting proteins were targeted to the motile compartments similar to the MyoB1 and MyoB2 compartments described in Arabidopsis (S1A Fig) [30]
Cytoplasmic streaming is ubiquitous in eukaryotes, its exact mechanism and functions have not been determined in any of the model organisms, from plants where it was discovered nearly 250 years ago [5,21] to fungi [38] to animals [6]
Summary
How molecules and large macromolecular complexes are properly distributed and positioned is one of the central problems of cell biology. In relatively small prokaryotic cells, which lack endomembrane compartments, diffusion modulated by the cell’s metabolic status is a major mechanism at work for trafficking of both small molecules and large complexes [1]. Mechanism of Cytoplasmic Streaming in Plants much larger eukaryotic cells, where targeted transport of organelles and carrier vesicles, ER dynamics and cytosolic intermixing involve cytoskeletal transport networks encompassing microtubules and actin microfilaments with associated molecular motors [2,3,4]. Transport can be achieved by at least two mechanisms: active transport by receptor-mediated attachment of cargo to molecular motors and passive transport with cytosol flow or cytoplasmic streaming. It stands to reason that to establish streaming, a directional flow of motor-associated cargoes is required [5,6,7], making passive transport dependent on motor-driven active transport
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
