Different subcellular localizations and functions of Arabidopsis myosin VIII

Abstract

BackgroundMyosins are actin-activated ATPases that use energy to generate force and move along actin filaments, dragging with their tails different cargos. Plant myosins belong to the group of unconventional myosins and Arabidopsis myosin VIII gene family contains four members: ATM1, ATM2, myosin VIIIA and myosin VIIIB.ResultsIn transgenic plants expressing GFP fusions with ATM1 (IQ-tail truncation, lacking the head domain), fluorescence was differentially distributed: while in epidermis cells at the root cap GFP-ATM1 equally distributed all over the cell, in epidermal cells right above this region it accumulated in dots. Further up, in cells of the elongation zone, GFP-ATM1 was preferentially positioned at the sides of transversal cell walls. Interestingly, the punctate pattern was insensitive to brefeldin A (BFA) while in some cells closer to the root cap, ATM1 was found in BFA bodies. With the use of different markers and transient expression in Nicotiana benthamiana leaves, it was found that myosin VIII co-localized to the plasmodesmata and ER, colocalized with internalized FM4-64, and partially overlapped with the endosomal markers ARA6, and rarely with ARA7 and FYVE. Motility of ARA6 labeled organelles was inhibited whenever associated with truncated ATM1 but motility of FYVE labeled organelles was inhibited only when associated with large excess of ATM1. Furthermore, GFP-ATM1 and RFP-ATM2 (IQ-tail domain) co-localized to the same spots on the plasma membrane, indicating a specific composition at these sites for myosin binding.ConclusionTaken together, our data suggest that myosin VIII functions differently in different root cells and can be involved in different steps of endocytosis, BFA-sensitive and insensitive pathways, ER tethering and plasmodesmatal activity.

A Comparative Study of the Involvement of 17 Arabidopsis Myosin Family Members on the Motility of Golgi and Other Organelles

“…and ATM2 (IQ tail in N.b.) with Golgi movement is in agreement with our previous observation that ATM1 colocalized with the ER (Golomb et al, 2008) and raises the possibility of an indirect regulation of Golgi motility via ER motion (Boevink et al, 1998;Runions et al, 2006;Hawes et al, 2008) that is driven by myosins . Interestingly, we have recently shown that Golgi bodies are physically attached to the ER (Sparkes et al, 2009), which could potentially be via a myosin scaffold at the ER-Golgi interface, and we have evidence that ER remodeling still occurs in the absence of the Golgi bodies (I.A.…”

“…Previous expression studies of fluorescent fusions to class VIII (Golomb et al, 2008) and class XI (Reisen and Hanson, 2007) myosins corroborate these subcellular locations. However, Li and Nebenfü hr (2007) found that MYA1 fusions occasionally colocated to Golgi bodies, and Reisen and Hanson (2007) did not observe XI-I tail on the nuclear envelope.…”

“…As for myosin VIII, immunostaining studies showed that it localized to the cell periphery at plant-specific structures such as plasmodesmata and cytokinetic cell plates (Reichelt et al, 1999;Baluska et al, 2001). Recent data from our laboratory and from others confirmed the presence of myosin VIII in plasmodesmata (Golomb et al, 2008) and the cell plate (Van Damme et al, 2004) and further provided evidence for its involvement with endocytosis (Golomb et al, 2008;Sattarzadeh et al, 2008) and its colocalization with the ER (Golomb et al, 2008). In addition, it was shown that myosin VIII is involved in the plasmodesmata targeting of the beet yellows virus protein Hsp70h (Avisar et al, 2008a).…”

“…Leaves of 3-week-old N.b. plants were infiltrated with the bacterial culture using a 1-mL syringe as described previously (Golomb et al, 2008). Expression of the fluorescent chimera in the leaf cells was analyzed after 48 h. N.t.…”

Inhibition of Tobacco Mosaic Virus Movement by Expression of an Actin-Binding Protein

“…7). We speculate that the inhibitory mechanism involves interference with class XI myosins; nevertheless, class VIII myosins may also have a role, since they are associated with PD (Reichelt et al, 1999;Volkmann et al, 2003;Golomb et al, 2008). Although specific inhibition of class VIII myosin cargo binding was reported to have no effect on the targeting of the TMV MP to PD (Avisar et al, 2008a), inhibiting the translocation of this myosin class along actin filaments could still lead to hindrance in the cellular pathway that supports the spread of infection.…”