Identification and intracellular functional characterization of myosin XI and VIII in the lycophyte Selaginella moellendorffii

MAIN CONCLUSION: Selaginella moellendorffii myosins retain conserved intracellular functions of known plant myosins, while lycophytes possess a unique myosin VIII with an extended neck domain. Research on plant myosins has primarily focused on model species, such as green algae, mosses, and seed plants. Here, we identified and cloned the myosin genes in Selaginella moellendorffii for the first time in the lycophytes. S. moellendorffii possessed two myosin XI genes and two myosin VIII genes. The cloned S. moellendorffii myosin (Sm myosin) VIII contained a neck domain approximately twice as long as those of previously identified plant myosin VIIIs. A BLASTP search using OneKP indicates that this myosin VIII is conserved throughout lycophytes. Transient expression of Sm myosin in Arabidopsis thaliana cultured cells and Nicotiana benthamiana leaves suggests that Sm myosin XI-2 is orthologous to A. thaliana myosin XI-K, which provides a motive force for cytoplasmic streaming. Sm myosin VIII was localized to the plasmodesmata, consistent with A. thaliana myosin VIII, ATM1 localization. This suggests the plasmodesmata-associated function of myosin VIII is conserved among vascular plants. Cis-regulatory elements and expression analyses further indicate that Sm myosin responds to environmental stress and participates in spore reproduction. Cumulatively, the intracellular and physiological functions of plant myosins are highly conserved in land plants, whereas myosin VIII exhibits structural characteristics unique to lycophytes. These findings provide valuable insights into the conservation and diversification of plant myosins, contributing to a better understanding of their evolutionary dynamics in vascular plants.