Reaching out: Myosin XIK aids root hair elongation in Arabidopsis

Research Areas:

Plant biology, Root hair growth, Arabidopsis thaliana, Myosin

Imaging Needs:

Protein co-localization

Imaging System (light and DIC microscopy):
  • Leica MZ16 FA stereomicroscope
  • Length measures: Leica DFC420 camera, 7.1X or 23X magnification
  • Growth rate time-lapse: Hamamatsu ORCA-ER CCD camera, 100X objective lens
  • NIH ImageJ and Improvisation Openlab 5 software
Imaging System (fluorescence microscopy):
  • Yellow, cyan and mCherry fluorescent proteins
  • Zeiss Axiovert 200M microscope
  • Chroma filter sets 52017 and 69308
  • 63x (1.4 NA) plan-apo oil immersion objective
  • Hamamatsu ORCA-ER CCD camera
  • NIH ImageJ and Improvisation Openlab software
Fine resolution, wide view

Learn out how the Hamamatsu ImagEM camera's enhanced low-light capability and precise localization helped Ashley Cadby and colleagues to visualize the synthesis of cell walls in living bacteria. Read now.

THE QUESTION

What role do myosins play in the growth of plan root hairs?

Root hairs are tube-shaped extrusions that extend from the outer layer of epidermal cells along the roots of plants and into the surrounding soil. They add surface area to the roots to increase uptake of water and minerals, and they excrete acid that solubilizes soil minerals into more easily absorbed ions.

Loss of root hairs, such as during repotting, leaves plants drooping until new hairs can be grown. The intracellular mechanisms driving root hair development are not well understood.

THE BARRIERS

In plant cells, myosin motor proteins play important roles in cytoplasmic streaming, ensuring appropriate distribution of molecules throughout the cells and contributing to the establishment of cell polarity.

Disruption of individual class XI myosin genes in Arabidopsis results in only mild phenotypes, likely due to overlapping activity of multiple class XI myosin paralogs. However, double and triple mutants, such as mya2 xib xik, show almost no root hair growth, and quadruple mutants result in dwarfed plants with abnormal actin structures.Understanding the role of individual myosin isoforms in root hair growth was complicated by the lack of single mutations with strong phenotypes.

THE SOLUTION

Myosin XIK of Arabidopsis thaliana Accumulates at the Root Hair Tip and Is Required for Fast Root Hair Growth
Eunsook Park and Andreas Nebenführ
PLoS One 2013; 8(10): e76745. PMCID: PMC3792037.

The observation that individual mutation of either the mya2 or the xik class XI myosins leads to a short root hair phenotype opened the door to understanding the role of these proteins in root hair elongation. Park and Nebenführ 1 observed root hair growth and protein localization in wild-type and xik mutant Arabidopsis seedlings. Time-lapse differential interference contrast microscopy using a Hamamatsu ORCA-ER CCD camera revealed that root hair growth slows and stops early in xik mutants. Images were taken every 30 seconds for 45 minutes to 1 hour, and repeated to capture growth from first signs of a new root hair through final length.

Using fluorescence microscopy with the Hamamatsu ORCA-ER camera, the researchers found that XIK protein co-localizes with several markers of intracellular vesicles at root hair tips. Interestingly, mutation of xik did not affect actin structure and corresponding vesicle transport, nor did the morphology of the root hairs look like mutations that are known to disrupt cellular polarity, leading the authors to speculate that XIK does not play a large role in maintaining polarity. Though lacking notable effects on vesicle transport and actin structure, xik mutants do show reduced actin filament rearrangement. The authors conclude that myosin XIK is required for normal actin dynamics and optimal root hair growth through activity in the subapical region of the growing root hair.

THE POSSIBILITIES

Park and Nebenführ used live-cell imaging with Hamamatsu’s ORCA-ER CCD camera to track root hair growth and co-localize myosin and vesicle proteins in living root hair tips. Learn how newer technology makes it possible to pinpoint features as small as 35–42 nanometers within a wider area of the living cell—read Exciting Insights into Cell Growth.

References

  1. Park and Nebenführ. Myosin XIK of Arabidopsis thaliana Accumulates at the Root Hair Tip and Is Required for Fast Root Hair Growth. PLoS One 2013; 8(10): e76745. PMCID: PMC3792037.
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