Abstract
Myosins and actin filaments in the actomyosin system act in concert in regulating cell structure and dynamics and are also assumed to contribute to plant gravitropic response. To investigate the role of the actomyosin system in the inflorescence stem gravitropism, we used single and multiple mutants affecting each of the 17 Arabidopsis myosins of class VIII and XI. We show that class XI but not class VIII myosins are required for stem gravitropism. Simultaneous loss of function of myosins XI1, XI2, and XIK leads to impaired gravitropic bending that is correlated with altered growth, stiffness, and insufficient sedimentation of gravity sensing amyloplasts in stem endodermal cells. The gravitropic defect of the corresponding triple mutant xi1 xi2 xik could be rescued by stable expression of the functional XIK:YFP in the mutant background, indicating a role of class XI myosins in this process. Altogether, our results emphasize the critical contributions of myosins XI in stem gravitropism of Arabidopsis.
Highlights
Myosins are a family of eukaryotic motor proteins with conserved structure that perform multiple functions in cell organization and motility
To analyze the role of myosins in gravity response of the inflorescence stems of Arabidopsis, we performed a gravitropism assay on myosin single, double, triple, and quadruple mutant lines
We analyzed myosin mRNA content of each homozygous T-DNA mutant line by reverse transcription followed by real-time PCR (RT-qPCR)
Summary
Myosins are a family of eukaryotic motor proteins with conserved structure that perform multiple functions in cell organization and motility. They use energy derived from ATP hydrolysis to slide along actin filaments. Arabidopsis myosins XI1, XI2, XIB, XIC, XIE, XIF, XIG, XII, and XIK have been reported to have overlapping roles in pollen tube and root hair elongation, trichome development, plant size, and organelle motility (Prokhnevsky et al, 2008; Peremyslov et al, 2010; Ojangu et al, 2012; Madison et al, 2015; Okamoto et al, 2015). We show that myosins XI are involved in stem gravitropism and discuss possible reasons underlying this phenotype
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