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First published online January 4, 2008; 10.1104/pp.107.113654 Plant Physiology 146:1109-1116 (2008) © 2008 American Society of Plant Biologists OPEN ACCESS ARTICLE
Two Class XI Myosins Function in Organelle Trafficking and Root Hair Development in Arabidopsis1,[OA]Department of Botany and Plant Pathology (V.V.P., A.I.P., D.A., V.V.D.) and Center for Genome Research and Biocomputing (V.V.D.), Oregon State University, Corvallis, Oregon 97331
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.
Myosins are signature molecular motors of eukaryotes that are involved in a broad spectrum of actin cytoskeleton-associated types of cellular dynamics (Vale, 2003  ). Comparative genomics revealed that myosins are conserved throughout the eukaryotic domain of life (Richards and Cavalier-Smith, 2005; Foth et al., 2006). Land plants possess two myosin classes, XI and VIII, each of which is evolutionary, related to animal and fungal class V myosins (Desnos et al., 2007), suggesting their origin was from a common ancestor that antedated the divergence of Plantae and Opisthokonts (Foth et al., 2006). Subsequent evolution of myosins was dominated by gene duplication and diversification that resulted in the presence of more than 10 myosin genes in all plant genomes sequenced so far (see accompanying article Avisar et al., 2008). In particular, Arabidopsis (Arabidopsis thaliana) encodes 13 class XI and four class VIII myosins (Reddy and Day, 2001). The studies that mostly involved cytoskeletal inhibitors have demonstrated the principal role of actomyosin motilty in plant cell dynamics including organelle trafficking, remodeling, and inheritance (Boevink et al., 1998; Nebenfuhr et al., 1999; Sheahan et al., 2004; Kim et al., 2005; Runions et al., 2006). Some of the class XI myosins were found in association with organelles suggesting their involvement in organelle transport (Wang and Pesacreta, 2004; Hashimoto et al., 2005; Li and Nebenfuhr, 2007; Reisen and Hanson, 2007). However, information on functional profiles of individual myosin motors is very limited. Two recent publications have demonstrated the role of Arabidopsis myosin XI-K in root hair growth (Ojangu et al., 2007), and implicated rice (Oryza sativa) myosin XI-B in pollen development (Jiang et al., 2007). Here we screen the gene knockouts of all 13 class XI myosins of Arabidopsis to show that, in addition to myosin XI-K, myosin XI-2 (MYA2) is also required for root hair development. Furthermore, we demonstrate that each of these two highly expressed myosins functions in the rapid movement of the Golgi stacks, peroxisomes, and mitochondria in roots and leaves. Interestingly, inactivation of the genes encoding the most closely related paralogs of myosins XI-K and XI-2 and myosins XI-1 (MYA1) and XI-B, respectively, did not impair root hair growth or organelle trafficking. These results indicate that evolution of myosins in plants combines opposing tendencies of functional specialization and functional redundancy.
Isolation of the Homozygous Knockout Lines Sixteen homozygous lines in which each of the 13 class XI myosin genes of Arabidopsis was inactivated by T-DNA insertion were obtained and the exact localization of the insert was determined by sequencing (Fig. 1A ; data not shown). Furthermore, inactivation of the target genes was demonstrated using semiquantitative reverse transcription (RT)-PCR (e.g. Fig. 1B). The corresponding mRNAs were undetectable by RT-PCR analysis, therefore confirming complete abolishment of myosin expression for each of the 16 knockout lines. To ensure that the observed phenotype is attributed solely to the inactivation of the myosin XI-K locus, line SALK_067972 was further backcrossed twice to the wild-type plant, and the homozygous progeny was selected and used for the experiments described below. In addition, two independent lines for myosin XI-K and three for myosin XI-2 genes were selected for further experiments to ensure that the observed phenotypes were due to the T-DNA insertion in the corresponding locus rather than to secondary site mutations. For both of the obtained independent myosin XI-K gene knockout lines, the lack of an expressed protein was confirmed using a polyclonal antibody specific to this myosin (Fig. 1C).
Inactivation of Myosins XI-2 and XI-K Induces Similar Defects in Root Hair Growth Inspection of the insertional lines in which each of the 13 class XI myosin genes present in Arabidopsis genome was inactivated (Fig. 1; data not shown) revealed no detectable developmental defects in the aerial organs of plants grown under normal conditions. Therefore, the seeds of each line were planted to vertical plates to screen for root morphology. Although the overall root sizes and shapes appeared normal in all knockout lines, four lines exhibited obvious defects in the elongation of the root hairs (Fig. 2A ). These lines were knockouts of two class XI myosin genes, namely, XI-2 and XI-K. Quantification of the root hair length for each of these lines revealed a dramatic reduction in the mean root hair length that varied from 28% to 40% of that in the parental Columbia line (Fig. 2B). Comparative analysis showed that the differences in the root hair length between each of these four knockout lines and the wild-type line were statistically significant with P < 0.001 for all lines.
Interestingly, analysis of the light-regulated chloroplast relocalization performed as described in an accompanying work by Avisar et al. (2008) revealed that none of the myosin gene knockouts exhibited observable defects in chloroplast movement (data not shown). This result suggested that several myosin motors may have overlapping functions in chloroplast movement. Alternatively, it is possible that although chloroplast movement requires intact actin cytoskeleton (Paves and Truve, 2007), it does not involve myosins.
To confirm the results of the gene knockout experiments by an independent approach and to examine the usefulness of the dominant negative inhibition of the myosin function that we used for Nicotiana benthamiana in an accompanying article (Avisar et al., 2008 Given that the principal function of myosin motors is physical translocation of various cargoes, our findings suggest that such translocation powered by myosins XI-2 and XI-K is required for the rapid polarized growth of the root hairs.
What are the cargoes transported by the myosins XI-2 and XI-K within the growing root hairs? To address this question, we studied trafficking of Golgi stacks and peroxisomes in the gene knockout lines that were transformed to express the fluorophore-tagged, organelle-specific reporters (Fig. 3, A–C ). The mitochondrial transport was examined using a vital fluorescent dye Rhodamine 123 (Fig. 3E). Organelle trafficking in the live root hairs was visualized by confocal microscopy and the resulting movies were used for computer-assisted organelle tracking and velocity measurements.
As expected, the predominant pattern of Golgi movement was along the root hair longitudinal axis (Fig. 3A). It should be noted, however, that not infrequently the neighboring individual Golgi stacks were moving in the opposite directions or with the drastically distinct velocities (data not shown). This pattern and a mean Golgi velocity of approximately 1 µm/s were very similar to those recently described for Arabidopsis root hairs (Campanoni et al., 2007 ). It seems, therefore, that Golgi stacks move independently of each other rather than in a uniform stream-like pattern. Strikingly, we found that inactivation of either myosin XI-2 or myosin XI-K resulted in an approximately 2-fold reduction in the mean velocity of the Golgi stacks and peroxisomes (Fig. 3D). In the case of mitochondria, the myosin XI-K knockout line exhibited more than 3-fold lower velocity than that in the wild type, whereas a less dramatic, approximately 1.5-fold velocity reduction was observed in the myosin XI-2 knockout line (Fig. 3F). In all cases, differences between the organelle velocities in knockout lines versus the parental Columbia line were statistically significant with P < 0.001. Taken together, these observations demonstrate that myosins XI-K and XI-2 each make a significant contribution into the rapid transport of Golgi stacks, peroxisomes, and mitochondria in the root hairs. This, however, does not necessarily imply that the defects in root hair growth seen in the corresponding knockout lines can be directly attributed to the slower organelle movement. To determine whether or not myosins XI-2 and XI-K are required for rapid organelle trafficking in organs other than root hairs, we examined motility of Golgi stacks and peroxisomes in the elongated epidermal cells found along the central vein on the leaf underside (Fig. 4B , central area). These elongated cells are most amenable to observing and measuring organelle movement in leaves. Interestingly, the mean velocity of these organelles in leaf cells was at least 30% greater than that in the root hairs (compare with Figs. 3D and 4D). Inactivation of either myosin XI-2 or myosin XI-K resulted in an approximately 3- to approximately 5-fold reduction of the mean velocity of Golgi stacks and peroxisomes (Fig. 4, A, C, and D), and also a stronger effect compared with that in the root hairs. The dominant negative inhibition of myosin XI-K closely mimicked the effect of the gene knockout, once again confirming the utility of this approach for the study of myosin function in plants (Fig. 4, A and D).
The mean velocity of mitochondria in the leaf cells was approximately 40% greater than that in the root hairs (compare with Figs. 3F and 4F). Interestingly, inactivation of the two myosin genes had distinct effects on the translocation of mitochondria: the myosin XI-2 gene knockout line showed only a moderate, although statistically significant (P = 0.045) reduction in the velocity of this organelle, whereas the myosin XI-K knockout line exhibited a drastic, 3.5-fold velocity reduction (Fig. 4, E and F). Collectively, these results demonstrated that two class XI myosins, XI-2 and XI-K, make comparable contributions to rapid trafficking of Golgi stacks and peroxisomes in the Arabidopsis roots and leaves. It seems, however, that myosin XI-K plays a more significant role in the translocation of mitochondria than myosin XI-2 and that this difference is more pronounced in leaves than in root hairs.
Phylogenetic analysis of plant myosins presented in Figure 1A of an accompanying article (Avisar et al., 2008
It was also found that transgenic expression of the myosin XI-1/GTD (Fig. 5H) had only moderate negative effects on the root hair growth (Fig. 5A) or on peroxisome trafficking (Fig. 5, F and G). Taken together, these observations indicate that myosins XI-B and XI-1 might play only a relatively minor role in the root hair development and organelle translocation in the presence of intact paralogous myosins XI-2 and XI-K.
It is well established that actin cytoskeleton dynamics plays a paramount role in the polarized growth of the root hair cells (Hepler et al., 2001 ; Carol and Dolan, 2002; Smith and Oppenheimer, 2005; Staiger and Blanchoin, 2006). However, there is only limited insight into the significance of the myosin-powered motility of vesicles and organelles for the elongation of the root hairs. In fact, only one class XI Arabidopsis myosin, XI-K, was recently implicated in this process (Ojangu et al., 2007), and even in this study, the potential role of this myosin in organelle movement has not been addressed. Here we describe systematic screening of all 13 class XI myosins of Arabidopsis for their potential functions in the root hair development. Using gene knockout and dominant negative inhibition approaches, we reveal that two class XI myosins, XI-2 and XI-K, are essential for the normal elongation of the root hairs. Inactivation of each of these myosins in four distinct insertion lines (Fig. 1) results in very similar phenotypes with a mean root hair length of approximately one-third that in the parental Columbia line (Fig. 2). In addition, we investigated the roles of myosins XI-2 and XI-K, and their most closely related paralogs, myosins XI-B and XI-1, in the trafficking of Golgi stacks, peroxisomes, and mitochondria in the root hairs. Conspicuously, we found that myosins XI-2 and XI-K are each required for the rapid movement of all three organelles (Fig. 3). Inactivation of the corresponding genes reduced the mean velocity of organelles from 1.5- to 3-fold depending on the organelle or myosin identity. In contrast, inactivation of the closely related, paralogous myosins XI-B and XI-1, had no detectable effects on either root hair growth or organelle motility (Fig. 5); additional work is needed to identify functions of these myosins.
The observed correlation in the roles of myosins XI-2 and XI-K in root hair growth and organelle trafficking suggests that the latter might be functionally required for the former. Indeed, the rapid movement of the Golgi stacks, peroxisomes, and mitochondria in a "reverse fountain" manner (Hepler et al., 2001
Recent insight into the mechanistic parallelism in the development of the root hairs and pollen (Hepler et al., 2001 We found that myosins XI-2 and XI-K are required for the rapid organelle trafficking not only in root hairs, but also in the leaves (Fig. 4). This conclusion resonates with the relatively high levels of these myosins in leaves (http://www.weigelworld.org/resources). In fact, myosins XI-2, XI-K, and XI-1 are the most abundant myosins in the entire Arabidopsis plants. Surprisingly, this abundance and major roles played by myosins XI-2 and XI-K in organelle movement do not translate into substantial defects in the development of leaves, stems, or flowers in the corresponding gene knockout lines. It appears that the reduction in the leaf organelle velocity in these lines is not critical for leaf development under normal growth conditions. Therefore, perhaps due to their rapid elongation, root hairs are a more sensitive indicator for the defects in organelle trafficking than the leaf cells.
The lack of major developmental defects in two myosin XI-2 knockout lines characterized here and in an additional line described elsewhere (Hashimoto et al., 2005
Rapid organelle trafficking is a hallmark of plant cell physiology that is traditionally referred to as "cytoplasmic streaming" (Hepler et al., 2001
On a broader scale, this work is relevant to the problem of the multigene families' evolution in eukaryotes: to what extent the lineage-specific expansion of these families is due to adaptation as opposed to stochastic gene birth and death processes (Lynch, 2007
T-DNA Insertion Mutants
Seeds of Arabidopsis (Arabidopsis thaliana) ecotype Columbia T-DNA insertion lines SALK_055785 and SAIL_632_D12 (At5g43900; myosin XI-2), SALK_067972 and WiscDsLox417C12 (At5g20490; myosin XI-K), SALK_113062 (At1g04160; myosin XI-B), SALK_019031 (At1g17580; myosin XI-1), SALK_082078 (At2g33240; myosin XI-D), SALK_072023 (At1g54560; myosin XI-E), SALK_018032 (At2g20290; myosin XI-G), SAIL_365_D03 (At4g28710; myosin XI-H), SALK_082443 (At4g33200; myosin XI-I), and SALK_063159 (At3g58160; myosin XI-J) were acquired from the Arabidopsis Biological Resource Center (Alonso et al., 2003 Rabbit polyclonal antiserum against synthetic oligopeptide AFSEAEARNSELATELENA-TRKAD corresponding to the amino acid residues 936 to 959 of the deduced sequence of the Arabidopsis myosin XI-K was custom-made by Genemed Synthesis and used for immunoblot analysis at 1:5,000 dilution.
Seeds were surface sterilized and grown on vertical plates containing 0.5x Murashige and Skoog medium, 5 mM MES, pH 5.8, 1% Suc, and 0.6% Phytogel under a 16-h light/8-h dark cycle. Root hair phenotypes of the 5-d-old seedlings were photographed using a Leica MZ6 stereozoom microscope equipped with a charge-coupled device camera and measured using the Image-Pro (Media Cybernetics) software. At least 200 root hairs from four or more individual plants were measured to determine the mean length for each line shown in Figures 2 and 5.
A Golgi-specific reporter was obtained by fusing rat
For visualization of live mitochondria in root hairs, seeds were germinated and grown for 5 d on the same medium supplemented with 50 nM of Rhodamine 123 (Invitrogen). A series of eight consecutive images was acquired using a 510 Meta (Zeiss) confocal microscope and was used to measure the organelle velocities. Samples were excited using Argon laser at 488 nm, emission signal was collected through a band-pass 505- to 530-nm filter. The Golgi stacks and peroxisomes were observed using the following configurations of excitation and emission filters, respectively: 488 and 508 nm for GFP, 513 and 527 nm for yellow fluorescent protein, and 587 and 610 nm for mCherry. For time-lapse experiments, the consecutive images were taken at 1-s intervals for mitochondria or 2 s for Golgi and peroxisomes. For the root hair and leaf epidermis observations, more than 150 and 300 individual organelles, respectively, were traced. Tracking and measurements of velocities of individual organelles was performed using the Volocity3.7.0 Classification software (Improvision; Image Processing and Vision Company). Statistical analysis of the data was done using t test and Excel software. Additional details of organelle trafficking analyses are provided in an accompanying work (Avisar et al., 2008
We are grateful to Eugene Koonin for critical reading of the manuscript, to Amit Gal-On for kindly providing lab space to D.A., and to Maria Ivanchenko and Rex Cole for their technical help. The authors acknowledge the confocal microscopy facility of the Oregon State University Center for Genome Research and Biocomputing. Received November 27, 2007; accepted December 24, 2007; published January 4, 2008.
1 This work was supported in part by a grant from the National Institutes of Health (GM053190 to V.V.D.), and by a Vaadia-Binational Agricultural Research and Development Postdoctoral Fellowship (award no. F1–354–2004 to D.A.) from the U.S.-Israel Binational Agricultural Research and Development Fund. The publication was made possible in part by support from the National Institutes of Health (grant no. 1S10RR107903–01). 
2 These authors contributed equally to the article. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Valerian V. Dolja (doljav{at}science.oregonstate.edu).
[OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.107.113654 * Corresponding author; e-mail doljav{at}science.oregonstate.edu.
Alonso JM, Stepanova AN, Leisse TJ, Kim CJ, Chen H, Shinn P, Stevenson DK, Zimmerman J, Barajas P, Cheuk R, et al (2003) Genome-wide insertional mutagenesis of Arabidopsis thaliana. Science 301: 653–657 Avisar D, Prokhnevsky AI, Makarova KS, Koonin EV, Dolja VV (2008) Myosin XI-K is required for rapid trafficking of Golgi stacks, peroxisomes, and mitochondria in leaf cells of Nicotiana benthamiana. Plant Physiol 146: 1098–1108 Boevink P, Oparka KJ, Santa Cruz S, Martin B, Betteridge A, Hawes C (1998) Stacks on tracks: the plant Golgi apparatus traffics on an actin/ER network. Plant J 15: 441–447[CrossRef][ISI][Medline] Campanoni P, Sutter JU, Davis CS, Littlejohn GR, Blatt MR (2007) A generalized method for transfecting root epidermis uncovers endosomal dynamics in Arabidopsis root hairs. Plant J 51: 322–330[CrossRef][Medline] Carol RJ, Dolan L (2002) Building a hair: tip growth in Arabidopsis thaliana root hairs. Philos Trans R Soc Lond B Biol Sci 357: 815–821[CrossRef][ISI][Medline] Cole RA, Fowler JE (2006) Polarized growth: maintaining focus on the tip. Curr Opin Plant Biol 9: 579–588[CrossRef][ISI][Medline] Curtis MD, Grossniklaus U (2003) A gateway cloning vector set for high-throughput functional analysis of genes in planta. Plant Physiol 133: 462–469 Desnos C, Huet S, Darchen F (2007) ‘Should I stay or should I go?’: myosin V function in organelle trafficking. Biol Cell 99: 411–423[CrossRef][Medline] Foth BJ, Goedecke MC, Soldati D (2006) New insights into myosin evolution and classification. Proc Natl Acad Sci USA 103: 3681–3686 Hashimoto K, Igarashi H, Mano S, Nishimura M, Shimmen T, Yokota E (2005) Peroxisomal localization of a myosin XI isoform in Arabidopsis thaliana. Plant Cell Physiol 46: 782–789 Hepler PK, Vidali L, Cheung AY (2001) Polarized cell growth in higher plants. Annu Rev Cell Dev Biol 17: 159–187[CrossRef][ISI][Medline] Holweg C, Nick P (2004) Arabidopsis myosin XI mutant is defective in organelle movement and polar auxin transport. Proc Natl Acad Sci USA 101: 10488–10493 Jiang SY, Cai M, Ramachandran S (2007) Oriza sativa myosin XI B controls pollen development by photoperiod-sensitive protein localizations. Dev Biol 304: 579–592[CrossRef][Medline] Kim H, Park M, Kim SJ, Hwang I (2005) Actin filaments play a critical role in vacuolar trafficking at the Golgi complex in plant cells. Plant Cell 17: 888–902 Li JF, Nebenfuhr A (2007) Organelle targeting of myosin XI is mediated by two globular tail subdomains with separate cargo binding sites. J Biol Chem 282: 20593–20602 Lynch M (2007) The origins of genome architecture. Sinauer Assoc., Inc., Sunderland, MA Mano S, Nakamori C, Hayashi M, Kato A, Kondo M, Nishimura M (2002) Distribution and characterization of peroxisomes in Arabidopsis by visualization with GFP: dynamic morphology and actin-dependent movement. Plant Cell Physiol 43: 331–341 Nebenfuhr A, Gallagher LA, Dunahay TG, Frohlick JA, Mazurkiewicz AM, Meehl JB, Staehelin L (1999) Stop-and-go movements of plant Golgi stacks are mediated by the acto-myosin system. Plant Physiol 121: 1127–1141 Nebenfuhr A, Staehelin LA (2001) Mobile factories: Golgi dynamics in plant cells. Trends Plant Sci 6: 160–167[CrossRef][ISI][Medline] Ojangu EL, Jarve K, Paves H, Truve E (2007) Arabidopsis thaliana myosin XIK is involved in root hair as well as trichome morphogenesis on stems and leaves. Protoplasma 230: 193–202[CrossRef][Medline] Paves H, Truve E (2007) Myosin inhibitors block accumulation movement of chloroplastsin Arabidopsis thaliana leaf cells. Protoplasma 230: 165–169[CrossRef][Medline] Reddy AS, Day IS (2001) Analysis of the myosins encoded in the recently completed Arabidopsis thaliana genome sequence. Genome Biol 2: RESEARCH0024[Medline] Reisen D, Hanson MR (2007) Association of six YFP-myosin XI-tail fusions with mobile plant cell organelles. BMC Plant Biol 7: 6[CrossRef][Medline] Richards TA, Cavalier-Smith T (2005) Myosin domain evolution and the primary divergence of eukaryotes. Nature 436: 1113–1118[CrossRef][Medline] Runions J, Brach T, Kuhner S, Hawes C (2006) Photoactivation of GFP reveals protein dynamics within the endoplasmic reticulum membrane. J Exp Bot 57: 43–50 Saint-Jore CM, Evins J, Batoko H, Brandizzi F, Moore I, Hawes C (2002) Redistribution of membrane proteins between the Golgi apparatus and endoplasmic reticulum in plants is reversible and not dependent on cytoskeletal networks. Plant J 29: 661–678[CrossRef][ISI][Medline] Sheahan MB, Rose RJ, McCurdy DW (2004) Organelle inheritance in plant cell division: the actin cytoskeleton is required for unbiased inheritance of chloroplasts, mitochondria and endoplasmic reticulum in dividing protoplasts. Plant J 37: 379–390[CrossRef][ISI][Medline] Shimmen T (2007) The sliding theory of cytoplasmic streaming: fifty years of progress. J Plant Res 120: 31–43[CrossRef][Medline] Smith LG, Oppenheimer DG (2005) Spatial control of cell expansion by the plant cytoskeleton. Annu Rev Cell Dev Biol 21: 271–295[CrossRef][ISI][Medline] Staiger CJ, Blanchoin L (2006) Actin dynamics: old friends with new stories. Curr Opin Plant Biol 9: 554–562[CrossRef][ISI][Medline] Taiz L, Ziegler E (2006) Plant Physiology, Ed 4. Sinauer Associates, Sunderland, MA Vale RD (2003) The molecular motor toolbox for intracellular transport. Cell 112: 467–480[CrossRef][ISI][Medline] Wang Z, Pesacreta TC (2004) A subclass of myosin XI is associated with mitochondria, plastids, and the molecular chaperone subunit TCP-1 in maize. Cell Motil Cytoskeleton 57: 218–232[CrossRef][ISI][Medline] Related articles in Plant Physiol.:
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-2,6-sialyltransferase (Saint-Jore et al., 2002
