GSE200917
The Class VIII myosin ATM1 is integral for root apical meristem function
Myosins are evolutionarily conserved motor proteins that interact with actin filaments to  regulate organelle transport, cytoplasmic streaming and cell growth. Plant specific Class XI  myosin proteins direct cell division and root organogenesis. However, the roles of Class VIII  myosin proteins in plant growth and development are less understood. Here, we investigated  the function of an auxin-regulated Class VIII myosin, Arabidopsis thaliana Myosin 1 (ATM1),  using genetics and live cell microscopy. ATM1 is a plasmodesmata-localized protein that is  enriched in actively dividing cells in the root apical meristem (RAM). Loss of ATM1 function  results in impaired primary root growth due to decreased RAM size and reduced cell  proliferation in a sugar dependent manner. Examination of stem cell marker line expression in  atm1-1 indicated impaired division of the lateral root cap and columella cells and a diminished  auxin response. Transcriptome analysis of atm1-1 linked these growth defects to dysregulation  of cell cycle and auxin pathway genes. Complementation of ATM1 loss-of- function mutant  restored root growth and cell cycle progression in the root meristem. Collectively, these results  provide novel evidence that ATM1 functions to influence cell proliferation and differentiation in  primary roots in response to auxin and sugar cues. Overall design: Col-0 (control) and atm1-1 (mutant) seedlings were grown on media supplemented with or without (mock) 15mM glucose or sucrose for 5 days (5DO). Three biological replicates were collected for each condition.