Abstract
The actomyosin system is conserved throughout eukaryotes. Although F-actin is essential for cell growth and plant development, roles of the associated myosins are poorly understood. Using multiple gene knockouts in Arabidopsis thaliana, we investigated functional profiles of five class XI myosins, XI-K, XI-1, XI-2, XI-B, and XI-I. Plants lacking three myosins XI showed stunted growth and delayed flowering, whereas elimination of four myosins further exacerbated these defects. Loss of myosins led to decreased leaf cell expansion, with the most severe defects observed in the larger leaf cells. Root hair length in myosin-deficient plants was reduced approximately 10-fold, with quadruple knockouts showing morphological abnormalities. It was also found that trafficking of Golgi and peroxisomes was entirely myosin dependent. Surprisingly, myosins were required for proper organization of F-actin and the associated endoplasmic reticulum networks, revealing a novel, architectural function of the class XI myosins. These results establish critical roles of myosin-driven transport and F-actin organization during polarized and diffuse cell growth and indicate that myosins are key factors in plant growth and development.
Highlights
The actin cytoskeleton is conserved in diverse unicellular and multicellular organisms and is important for a variety of cellular processes (Embley and Martin, 2006)
We reveal a novel role of class XI myosins in the organization of the actin cytoskeleton and endoplasmic reticulum (ER)
In the xi-k xi-2 xi-b xi-i 4KO mutant exhibited abnormal initiation of an additional root hair near the middle of the cell. These results indicated that class XI myosins contribute to the proper initiation of root hair growth and in the transition from bud swelling to tip growth
Summary
The actin cytoskeleton is conserved in diverse unicellular and multicellular organisms and is important for a variety of cellular processes (Embley and Martin, 2006). Due to their large size and compartmentalized organization, eukaryotic cells use active transport of macromolecules, vesicles, and organelles to coordinate cellular functions. The actin cytoskeleton, rather than microtubules, plays a principal role in the organization of the plant cell interior, including the endomembrane system and trafficking network (Smith and Oppenheimer, 2005; Szymanski and Cosgrove, 2009). Plant cells exhibit F-actin dynamics characterized by microfilament growth and severance rates that are much higher than those in yeast or animal cells (Staiger et al, 2009)
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