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. 2008 Mar;146(3):1109-16.
doi: 10.1104/pp.107.113654. Epub 2008 Jan 4.

Two class XI myosins function in organelle trafficking and root hair development in Arabidopsis

Valera V Peremyslov  1 , Alexey I Prokhnevsky, Dror Avisar, Valerian V Dolja
Affiliations

Two class XI myosins function in organelle trafficking and root hair development in Arabidopsis

Valera V Peremyslov et al. Plant Physiol. 2008 Mar.

Abstract

Multigene families encoding class XI myosins are conserved in higher plants, however, little information is available on specific functions of these ubiquitous molecular motors. We isolated gene knockout mutants for all 13 class XI myosins present in Arabidopsis (Arabidopsis thaliana) genome. Inactivation of 11 myosin genes resulted in no discernible phenotypes under the normal growth conditions. In contrast, the knockouts of the remaining two myosin genes, XI-2 (formerly MYA2) and XI-K, exhibited similar defects in root hair elongation suggesting that the myosin-driven motility plays a significant role in a polar tip growth. Strikingly, inactivation of each of these myosins also reduced trafficking of Golgi stacks, peroxisomes, and mitochondria in root hairs and in leaf epidermal cells. These results indicate that myosins XI-K and XI-2 play major and overlapping roles in the cell dynamics in Arabidopsis and highlight the redundant nature of myosin function in plants.

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Figures

Figure 1.
Figure 1.
A, Diagrams of the four Arabidopsis myosin class XI genes with the positions of the T-DNA insertions. White boxes represent exons, black lines represent introns, and gray bars correspond to the 5′ and 3′ untranslated regions. Designations of each line are shown above the corresponding T-DNA insertion sites (black triangles). Sizes of exons and introns are drawn to scale using Gene Structure Display Server (http://gsds.cbi.pku.edu.cn). The diagram corresponding to the gene At5g20490 (myosin XI-K) was modified to accommodate corrections in the exon structure (Ojangu et al., 2007). B, Semiquantitative RT-PCR analysis of the insertion line SALK_055785 in which the myosin XI-2 gene was inactivated. Primers complementary to sites flanking the insertion site in the myosin XI-2 mRNA (lines under XI-2 in the image) or complementary to two regions within the myosin XI-K mRNA (lines under XI-K) were used. In the control, the RNA used for analysis was isolated from the parental Columbia line. The expected position of the DNA amplification products for each mRNA is shown by an arrow. C, Immunoblot analysis of the protein extracts from the control (Col in the image) and myosin XI-K knockout plants using specific polyclonal antibody. Samples from two plants for each line are shown.
Figure 2.
Figure 2.
Root hair development in the knockout mutants and transgenic plants expressing a dominant negative mutant of the myosin XI-K. A, Typical images of the roots for the control (Columbia) and four knockout lines are shown as indicated. XI-K/GTD is a transgenic line expressing GTD of the myosin XI-K. B, Analysis of the mean root hair length for the lines shown (A). C, Immunoblot analysis of the HA epitope-tagged XI-K/GTD expression using HA-specific monoclonal antibody. Samples were from a control plant (C in the image) and plants representing three independent transgenic lines (1, 2, and 8). Positions of two size markers (molecular mass in kilodaltons) are shown by arrows.
Figure 3.
Figure 3.
Roles of myosins XI-2 and XI-K in organelle trafficking in root hairs. A, C and E, Representative images of the indicated organelles (top rows) and paths of individual organelles plotted relative to a common origin (bottom rows; each axis is 100 μm). B, Images of the roots of parental and knockout lines transformed with the Golgi-specific GFP reporter. D, Mean velocities of the Golgi stacks and peroxisomes. F, Mean velocities of mitochondria.
Figure 4.
Figure 4.
Roles of myosins XI-2 and XI-K in organelle trafficking in leaves. A, C, and E, Representative images of the indicated organelles (top rows) and paths of individual organelles plotted relative to a common origin (bottom rows; each axis is 100 μm). B, Image of the leaf vein in the Columbia line transformed with the Golgi-specific GFP reporter showing a file of elongated epidermal cells used for organelle tracking. D, Mean velocities of the Golgi stacks and peroxisomes. F, Mean velocities of mitochondria.
Figure 5.
Figure 5.
Myosins XI-B and XI-1 do not play significant roles in root hair development and organelle movement. A, Analysis of the mean root hair length for the indicated gene knockout mutant lines and transgenic line that expresses XI-1/GTD. B, D and F, Paths of individual organelles plotted relative to a common origin (each axis is 100 μm). C and E, Mean velocities of mitochondria in root hairs and leaf epidermal cells, respectively. G, Mean velocities of the peroxisomes in leaf epidermal cells. H, Immunoblot analysis of the HA epitope-tagged XI-1/GTD expression using HA-specific monoclonal antibody. Samples were from a control plant (C, Columbia in the image) and plants representing three independent transgenic lines (1, 6, and 7). Positions of two size markers (molecular mass in kilodaltons) are shown by arrows.
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