RETRACTED: Arabidopsis myosin XI mutant is defective in organelle movement and polar auxin transport

Abstract

Myosins are eukaryotic molecular motors moving along actin filaments. Only a small set of myosin classes is present in plants, in which myosins have been found to play a role in cytoplasmic streaming and chloroplast movement. Whereas most studies have been done on green algae, more recent data suggest a role of higher plant myosin at the postcytokinetic cell wall. Here we characterize a loss-of-function mutation for a myosin of plant-specific class XI and demonstrate myosin functions during plant development in Arabidopsis. T-DNA insertion in MYA2 caused pleiotropic effects, including flower sterility and dwarf growth. Elongation of epidermal cells, such as in hypocotyls and anther filaments, was reduced by up to 50% of normal length. This effect on anther filaments is responsible for flower sterility. In the meristems of root tips, it was evident that cell division was delayed and that cell plates were mislocated. Like zwichel, a kinesin-related mutation causing two-branched trichomes, the mya2 knockout causes branching defects, but here the trichomes remained unbranched. Growth was also impaired in pollen tubes and root hairs, cells that are highly dependent on vesicle transport. A failure in vesicle flow could be directly confirmed, because cytoplasmic streaming of vesicles and, more so, of large endoplasmic reticulum-based organelles was slowed. The defect in vesicle trafficking was accompanied by failures in basipetal auxin transport, measured in stem segments of inflorescences. This result strongly suggests a causal link between auxin-dependent processes and the distribution of vesicles and membrane-bound molecules by plant myosin

A Role for F-Actin in Hexokinase-Mediated Glucose Signaling

“…This pattern of filament rearrangement is different from that following treatment of etiolated coleoptiles with auxin or light, which also were visualized with a GFP-talin construct (Holweg et al, 2004). Whereas both light and Glc treatments cause a loss of fine mesh filaments, light treatment in the study by Holweg et al (2004) resulted in the realignment of actin into dispersed longitudinal strands that lack the extensive bundling that we observed following short-term Glc treatment. We further have shown that long-term Glc treatment that causes arrested seedling development resulted in further alterations in F-actin organization.…”

Myosin XI-K Is Required for Rapid Trafficking of Golgi Stacks, Peroxisomes, and Mitochondria in Leaf Cells of Nicotiana benthamiana

“…The fastest, among known molecular motors, processive motion supported by myosin XI-2 ortholog from Nicotiana benthamiana suggested that it might play a role in cytoplasmic streaming (Tominaga et al, 2003). It was also reported that inactivation of the XI-2 (same as MYA2) gene in Arabidopsis resulted in a slower movement of certain vesicles and severe developmental abnormalities (Holweg and Nick, 2004). However, because two independent studies, including an accompanying article (Peremyslov et al, 2008), failed to reproduce the latter phenotype (Hashimoto et al, 2005), its significance remains unclear.…”

Plant synapses: actin-based domains for cell-to-cell communication

“…Subsequently, such auxin-enriched vesicles act as carriers for the quantal release of auxin by means of exocytosis in a neurotransmitter-like mode [15,17]. In accordance with this 'neuronal' concept of auxin export, defects in vesicle trafficking in a myosin XI mutant of Arabidopsis are accompanied by failures of the basipetal auxin transport [38].…”