The ability of developing seedlings to respond and adapt to diverse environmental conditions including light is critical for their emergence and establishment (Benvenuti et al., 2001; Forcella et al., 2000; Salter et al., 2003; Yu and Huang, 2017). Cell expansion within the hypocotyl optimizes light and energy capture by the cotyledons, and enables the transition to autotrophic status (Botterweg-Paredes et al., 2020; Dowson‐Day and Millar, 1999; Oh et al., 2013). Hypocotyl elongation is regulated by multiple factors including temperature, phytohormones, circadian clock and light (Dowson‐Day and Millar, 1999; Ma et al., 2016; Procko et al., 2014; Reed et al., 2018; Yu and Huang, 2017). Endogenous and exogenous sugars are also important regulators of hypocotyl cell expansion (Lilley et al., 2012; Liu et al., 2011; Pfeiffer and Kutschera, 1995; Simon et al., 2018b; Singh et al., 2017; Zhang et al., 2010, 2015). Under constant darkness, the interaction between plant hormones such as brassinosteroid and gibberellin and sugar signalling is proposed to stimulate increase in hypocotyl length (Simon et al., 2018b; Zhang et al., 2010, 2015). Hypocotyl phenotypes are important tools in plant biology as they have been used to screen for mutants with altered responses to light and sugar signalling and some of the identified genes have revolutionized plant research (Nakano, 2019). In multicellular organisms, actomyosin-dependent transport constitutes an essential component of the cellular structure and dynamics (Duan and Tominaga, 2018; Kurth et al., 2017; Peremyslov et al., 2010). The Arabidopsis genome encodes 17 myosins classified into two distantly-related groups comprising 4 class VIII myosins and 13 class XI plant myosins (Haraguchi et al., 2019; Reddy and Day, 2001; Ryan and Nebenführ, 2018). The plant-specific-myosin XI has been implicated in diverse developmental processes (Cai et al., 2014), but the contribution of members of class VIII myosins including myosin1/ATM1 to plant development stills remains elusive.