Characterization of ancestral myosin XI from Marchantia polymorpha by heterologous expression in Arabidopsis thaliana

Abstract

Previous studies have revealed duplications and diversification of myosin XI genes between angiosperms and bryophytes; however, the functional differentiation and conservation of myosin XI between them remain unclear. Here, we identified a single myosin XI gene from the liverwort Marchantia polymorpha (Mp). The molecular properties of Mp myosin XI are similar to those of Arabidopsis myosin XIs responsible for cytoplasmic streaming, suggesting that the motor function of myosin XI is able to generate cytoplasmic streaming. In cultured Arabidopsis cells, transiently expressed green fluorescent protein (GFP)-fused Mp myosin XI was observed as some intracellular structures moving along the F-actin. These intracellular structures were co-localized with motile endoplasmic reticulum (ER) strands, suggesting that Mp myosin XI binds to the ER and generates intracellular transport in Arabidopsis cells. The tail domain of Mp myosin XI was co-localized with that of Arabidopsis myosin XI-2 and XI-K, suggesting that all these myosin XIs bind to common cargoes. Furthermore, expression of GFP-fused Mp myosin XI rescued the defects of growth, cytoplasmic streaming and actin organization in Arabidopsis multiple myosin XI knockout mutants. The heterologous expression experiments demonstrated the cellular and physiological competence of Mp myosin XI in Arabidopsis. However, the average velocity of organelle transport in Marchantia rhizoids was 0.04 AE 0.01 lm s À1 , which is approximately one-hundredth of that in Arabidopsis cells. Taken together, our results suggest that the molecular properties of myosin XI are conserved, but myosin XI-driven intracellular transport in vivo would be differentiated from bryophytes to angiosperms.

Plant-specific armadillo repeat kinesin directs organelle transport and microtubule convergence to promote tip growth

“…In Arabidopsis , myosin XI-i promotes nuclear motility in the mature cells through interaction with nuclear membrane proteins WIT1/2 39 , whereas rapid acropetal nuclear movement in growing root hairs could occur in the absence of myosin XI-i and microtubules are required for stable nuclear migration 40 , suggesting that both actin- and microtubule-based motor proteins participate in this process. Although myosin function remains unclear in M. polymorpha , molecular activity of myosin XI is well conserved, but the velocity of organelle motility is very low compared with that in flowering plants 41 . Hence, actin-myosin system is not the main transport machinery in rhizoids.…”