Single-point ACT2 gene mutation in the Arabidopsis root hair mutant der1-3 affects overall actin organization, root growth and plant development

Abstract

Background and AimsThe actin cytoskeleton forms a dynamic network in plant cells. A single-point mutation in the DER1 (deformed root hairs1) locus located in the sequence of ACTIN2, a gene for major actin in vegetative tissues of Arabidopsis thaliana, leads to impaired root hair development (Ringli C, Baumberger N, Diet A, Frey B, Keller B. 2002. ACTIN2 is essential for bulge site selection and tip growth during root hair development of Arabidopsis. Plant Physiology129: 1464–1472). Only root hair phenotypes have been described so far in der1 mutants, but here we demonstrate obvious aberrations in the organization of the actin cytoskeleton and overall plant development.MethodsOrganization of the actin cytoskeleton in epidermal cells of cotyledons, hypocotyls and roots was studied qualitatively and quantitatively by live-cell imaging of transgenic lines carrying the GFP-FABD2 fusion protein and in fixed cells after phalloidin labelling. Patterns of root growth were characterized by FM4-64 vital staining, light-sheet microscopy imaging and microtubule immunolabelling. Plant phenotyping included analyses of germination, root growth and plant biomass.Key ResultsSpeed of germination, plant fresh weight and total leaf area were significantly reduced in the der1-3 mutant in comparison with the C24 wild-type. Actin filaments in root, hypocotyl and cotyledon epidermal cells of the der1-3 mutant were shorter, thinner and arranged in more random orientations, while actin bundles were shorter and had altered orientations. The wavy pattern of root growth in der1-3 mutant was connected with higher frequencies of shifted cell division planes (CDPs) in root cells, which was consistent with the shifted positioning of microtubule-based preprophase bands and phragmoplasts. The organization of cortical microtubules in the root cells of the der1-3 mutant, however, was not altered.ConclusionsRoot growth rate of the der1-3 mutant is not reduced, but changes in the actin cytoskeleton organization can induce a wavy root growth pattern through deregulation of CDP orientation. The results suggest that the der1-3 mutation in the ACT2 gene does not influence solely root hair formation process, but also has more general effects on the actin cytoskeleton, plant growth and development.

The botanical multiverse of Peter Barlow

“…This study strongly implies a morphogenetic roles of the ARP2/3 complex in cell wall synthesis and polar auxin transport. Vaškebová et al (2018) analyzed the roles of ACTIN2, which is essential for bulge site selection and tip growth of root hairs [54]. Importantly, they investigated aspects of the cytoskeleton and plant growth in addition to effects of this root-hair deformation in the der1-3 mutant of Arabidopsis.…”

“…Although cortical microtubule organisation in root cells was not affected, the wavy pattern of root growth in the mutants was associated with higher frequencies of shifted cell division planes, which is consistent with shifts in positioning of microtubule-based pre-prophase bands and phragmoplasts. Vaškebová et al [54] therefore propose that the ACT2 mutation in the der1-3 mutant doesn't only affect root hair formation, but also has effects more generally on plant growth and development via the actin cytoskeleton. Such work continues to adds to our growing appreciation of the multitude of developmental processes in which the cytoskeletonin all its myriad componentsis involved in the life of the plant.…”

An overview of plant division‐plane orientation

“…Tansley insight New Phytologist defects in division-plane orientation (Mineyuki & Palevitz, 1990;McDowell et al, 1996;Sano et al, 2005;Rasmussen et al, 2011a;Va skebov a et al, 2017). PPB actin-microtubule interactions are possibly mediated by actin and microtubule-binding proteins that localize to the PPB, such as formins (Li et al, 2010), Myosin VIII (Wu & Bezanilla, 2014), or kinesins (Buschmann et al, 2011;Klotz & Nick, 2012;Schneider & Persson, 2015;Tian et al, 2015;Walter et al, 2015;Tseng et al, 2017;Yamada et al, 2017).…”

Cytoskeletal organization in isolated plant cells under geometry control

“…We next try to challenge the robustness of the actin response to shape by testing if an alteration in actin polymerization affected its organization in response to shape. The act2 mutant is known to show disrupted actin polymerization and cells in the mutant exhibit shorter actin filaments (Nishimura et al 2003;Vaškebová et al 2018) . We performed experiments on protoplasts of act2-5 mutants expressing the FABD-GFP reporter for actin (fig4a-b).…”