TITLE:
The Motor Kinesin 4II Is Important for Growth and Chloroplast Light Avoidance in the Moss Physcomitrella patens
AUTHORS:
Daniel MacVeigh-Fierro, Erkan Tüzel, Luis Vidali
KEYWORDS:
Microtubules, Cytoskeleton, Chloroplast Motility, Polarization, Photo-Relocation
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.4,
March
30,
2017
ABSTRACT: Understanding how plant cells adapt dynamically to
changes in the environment is a fundamental problem of plant biology. Under
many conditions, plant cells respond to environmental changes by modifying
their intracellular organization. A critical example of intracellular
reorganization is chloroplast photo-relocation, which is required for optimal
energy harvesting and avoiding photodamage. A key system responsible for the
spatial organization of intracellular components is the microtubule
cytoskeleton and its associated motor proteins, kinesins. Here we tested the
hypothesis that members of the kinesin 4II subfamily are important for
chloroplast photo-relocation in the moss Physcomitrella patens. Most
land plants, including P. patens, use an actin cytoskeleton-dependent
mechanism to transport chloroplasts in response to light. In addition to the
actin-based system, P. patens can also transport chloroplasts via a
microtubule-dependent mechanism, which is absent in flowering plants. Here, we
used a P. patens line that contains an inducible RNAi system to silence
all three kinesin 4-II genes present in this moss and evaluated their
participation in the microtubule-dependent chloroplast light avoidance
response. Because we found a significant effect on cell growth when kinesin
4IIs are silenced, we took advantage of the inducible system to establish a
reproducible and quantitative assay to evaluate chloroplast photo-relocation in
full-grown cells. Using a laser scanning confocal-based chloroplast light
avoidance response assay, we found a reduction in chloroplast motility when
kinesin 4IIs were silenced. Hence, in addition to identifying a role for
kinesin 4II proteins in protonemal cell growth, our results strongly support
the hypothesis that these kinesins play an important role in the chloroplast
light avoidance response.