Myosin XIK is a major player in cytoplasm dynamics and is regulated by two amino acids in its tail

It has recently been found that among the 17 Arabidopsis myosins, six (XIC, XIE, XIK, XI-I, MYA1, and MYA2) have a major role in the motility of Golgi bodies and mitochondria in Nicotiana benthamiana and Nicotiana tabacum. Here, the same dominant negative tail fragments were also found to arrest the movement of Gogi bodies when transiently expressed in Arabidopsis plants. However, when a Golgi marker was transiently expressed in plants knocked out in these myosins, its movement was dramatically inhibited only in the xik mutant. In addition, a tail fragment of myosin XIK could inhibit the movement of several post-Golgi organelles, such as the trans-Golgi network, pre-vacuolar compartment, and endosomes, as well as total cytoplasmic streaming, suggesting that myosin XIK is a major player in cytoplasm kinetics. However, no co-localization of myosin tails with the arrested organelles was observed. Several deletion truncations of the myosin XIK tail were generated to corroborate function with localization. All deletion mutants possessing an inhibitory effect on organelle movement exhibited a diffuse cytoplasmic distribution. Point mutations in the tail of myosin XIK revealed that Arg1368 and Arg1443 are essential for its activity. These residues correspond to Lys1706 and Lys1779 from mouse myosin Va, which mediate the inhibitory head–tail interaction in this myosin. Therefore, such an interaction might underlie the dominant negative effect of truncated plant myosin tails and explain the mislocalization with target organelles

The Making of a Compound Inflorescence in Tomato and Related Nightshades

Variation in the branching of plant inflorescences determines flower number and, consequently, reproductive success and crop yield. Nightshade (Solanaceae) species are models for a widespread, yet poorly understood, program of eudicot growth, where short side branches are initiated upon floral termination. This “sympodial” program produces the few-flowered tomato inflorescence, but the classical mutants compound inflorescence (s) and anantha (an) are highly branched, and s bears hundreds of flowers. Here we show that S and AN, which encode a homeobox transcription factor and an F-box protein, respectively, control inflorescence architecture by promoting successive stages in the progression of an inflorescence meristem to floral specification. S and AN are sequentially expressed during this gradual phase transition, and the loss of either gene delays flower formation, resulting in additional branching. Independently arisen alleles of s account for inflorescence variation among domesticated tomatoes, and an stimulates branching in pepper plants that normally have solitary flowers. Our results suggest that variation of Solanaceae inflorescences is modulated through temporal changes in the acquisition of floral fate, providing a flexible evolutionary mechanism to elaborate sympodial inflorescence shoots

Different subcellular localizations and functions of Arabidopsis myosin VIII-6

Ocal microscopy. A. Root of 5-day-old seedling. Scale bar: 50 μm. B. Lateral root of 20-day-old seedling. Scale bar: 20 μm. C(1) and C(2). Two images of the same 20-day-old seedling root. C(1) shows the root cap, scale bar: 20 μm, and C(2) shows the upper part. Scale bar: 50 μm. A similar pattern of GFP-ATM1 localization is seen in all roots: diffuse at the root cap, then dots, then more polarized organization along the transverse sides. D. GFP-ATM1 in root hair, scale bar: 10 μm. Arrows show the direction of the root caps.<p><b>Copyright information:</b></p><p>Taken from "Different subcellular localizations and functions of Arabidopsis myosin VIII"</p><p>http://www.biomedcentral.com/1471-2229/8/3</p><p>BMC Plant Biology 2008;8():3-3.</p><p>Published online 8 Jan 2008</p><p>PMCID:PMC2275265.</p><p></p

A Comparative Study of the Involvement of 17 Arabidopsis Myosin Family Members on the Motility of Golgi and Other Organelles1[W][OA]

Gene families with multiple members are predicted to have individuals with overlapping functions. We examined all of the Arabidopsis (Arabidopsis thaliana) myosin family members for their involvement in Golgi and other organelle motility. Truncated fragments of all 17 annotated Arabidopsis myosins containing either the IQ tail or tail domains only were fused to fluorescent markers and coexpressed with a Golgi marker in two different plants. We tracked and calculated Golgi body displacement rate in the presence of all myosin truncations and found that tail fragments of myosins MYA1, MYA2, XI-C, XI-E, XI-I, and XI-K were the best inhibitors of Golgi body movement in the two plants. Tail fragments of myosins XI-B, XI-F, XI-H, and ATM1 had an inhibitory effect on Golgi bodies only in Nicotiana tabacum, while tail fragments of myosins XI-G and ATM2 had a slight effect on Golgi body motility only in Nicotiana benthamiana. The best myosin inhibitors of Golgi body motility were able to arrest mitochondrial movement too. No exclusive colocalization was found between these myosins and Golgi bodies in our system, although the excess of cytosolic signal observed could mask myosin molecules bound to the surface of the organelle. From the preserved actin filaments found in the presence of enhanced green fluorescent protein fusions of truncated myosins and the motility of myosin punctae, we conclude that global arrest of actomyosin-derived cytoplasmic streaming had not occurred. Taken together, our data suggest that the above myosins are involved, directly or indirectly, in the movement of Golgi and mitochondria in plant cells

Different subcellular localizations and functions of Arabidopsis myosin VIII-0

P starting from the ATG and a reverse primer corresponding to the 3' end of ATM1 including its stop codon. The size of the expected fragment was 1734 bp. The template DNA was as follows: Lane 1. DNA from transgenic plants expressing GFP-ATM1(IQ-tail). Lane 2. DNA from wt plants. Lane 3. DNA from the plasmid used to generate the transgenic plants. Lane 4. Molecular weight markers. B. Western blot analysis showing sizes and levels of the expressed transgenes: Lane 1. GFP alone. Lane 2. GFP-ATM1(IQ-tail). Detection was performed with anti-GFP antibody.<p><b>Copyright information:</b></p><p>Taken from "Different subcellular localizations and functions of Arabidopsis myosin VIII"</p><p>http://www.biomedcentral.com/1471-2229/8/3</p><p>BMC Plant Biology 2008;8():3-3.</p><p>Published online 8 Jan 2008</p><p>PMCID:PMC2275265.</p><p></p

Different subcellular localizations and functions of Arabidopsis myosin VIII-2

D with a confocal microscope. A-B. Cells with GFP-ATM1(IQ-tail) organized in dots (arrows). A. GFP-ATM1. B. BFA bodies formed in these cells, shown by FM4-64. Note that the dotted pattern is not disrupted by the treatment (arrows). C. Overlay of A and B. Scale bar 10 μm. D-F Showing cells near the root cap where ATM1 is found in BFA bodies. D. GFP-ATM1, E. BFA bodies stained by FM4-64, F. overlay of D and E. Scale bar 10 μm. All images in this figure are composed of one optic section.<p><b>Copyright information:</b></p><p>Taken from "Different subcellular localizations and functions of Arabidopsis myosin VIII"</p><p>http://www.biomedcentral.com/1471-2229/8/3</p><p>BMC Plant Biology 2008;8():3-3.</p><p>Published online 8 Jan 2008</p><p>PMCID:PMC2275265.</p><p></p

Different subcellular localizations and functions of Arabidopsis myosin VIII-4

ATM1(IQ-tail) (dots of 980 ± 145 nm in diameter). B. FM4-64. C. Overlay of A and B (1 optic section). D. GFP-ATM1(IQ-tail) (dots of 630 ± 60 nm). E. FYVE-DsRED. F. Overlay of D and E (1 optic section). G. RFP-ATM1(IQ-tail) (dots of 300 ± 100, colored green for ease of demonstration). H. GFP-ARA7 (colored magenta for ease of demonstration). I. Overlay of G and H (1 optic section). J. RFP-ATM1(IQ-tail) (dots of 570 ± 75 nm, colored green for ease of demonstration). K. ARA6-GFP (colored magenta for ease of demonstration). L. Overlay of J. and K (1 optic section). Arrows show co-localization. Scale bars 5 μm. The microscope focus in A-I was in the cytoplasm while the focus in J-L was on the plasma membrane.<p><b>Copyright information:</b></p><p>Taken from "Different subcellular localizations and functions of Arabidopsis myosin VIII"</p><p>http://www.biomedcentral.com/1471-2229/8/3</p><p>BMC Plant Biology 2008;8():3-3.</p><p>Published online 8 Jan 2008</p><p>PMCID:PMC2275265.</p><p></p