Abstract
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.
Highlights
Gene families with multiple members are predicted to have individuals with overlapping functions
Genevestigator analysis of expression patterns of Arabidopsis myosins revealed that myosins ATM2 and VIIIB from the group of myosin VIII and myosins XI-A, XI-B, XI-C, XI-D, XI-E, and XI-J are expressed at high levels in pollen
Apart from mutants of myosin XI-K and MYA2, all other family members of myosin XI had no observable phenotypes, excluding a moderate decrease in peroxisome movement observed in mya1 knockout plants and in plants expressing the MYA1 dominant negative globular tail domain (Peremyslov et al, 2008)
Summary
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. The Arabidopsis myosins contain a conserved motor domain with ATPase and actin-binding activities, a number of IQ domains that bind myosin light chains, a coiled-coil domain for dimerization, and a specific tail that binds different cargo (Kinkema and Schiefelbein, 1994; Tominaga et al, 2003). Using these functional domains, myosins convert chemical energy from ATP hydrolysis into physical movement along actin fibers, carrying with. It was shown that myosin VIII is involved in the plasmodesmata targeting of the beet yellows virus protein Hsp70h (Avisar et al, 2008a)
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