Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University Olomouc, Olomouc, Czech Republic.
Ann Bot. 2018 Nov 3;122(5):889-901. doi: 10.1093/aob/mcx180.
The 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.
Organization 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.
Speed 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.
Root 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.
植物细胞中的肌动蛋白细胞骨架形成一个动态网络。位于拟南芥营养组织中主要肌动蛋白基因 ACTIN2 序列中的 DER1（畸形根毛 1）基因的单点突变导致根毛发育受损（Ringli C、Baumberger N、Diet A、Frey B、Keller B. 2002. ACTIN2 是拟南芥根毛发育中膨大部分选择和尖端生长所必需的。植物生理学 129: 1464-1472）。到目前为止，在 der1 突变体中只描述了根毛表型，但在这里，我们证明了肌动蛋白细胞骨架的整体组织和植物发育的明显异常。
通过携带 GFP-FABD2 融合蛋白的转基因系的活细胞成像和鬼笔环肽标记后固定细胞的定性和定量研究，研究了子叶、下胚轴和根表皮细胞中肌动蛋白细胞骨架的组织。通过 FM4-64 活染、光片显微镜成像和微管免疫标记来描述根生长模式。植物表型分析包括发芽、根生长和植物生物量分析。
与 C24 野生型相比，der1-3 突变体的发芽速度、植物鲜重和总叶面积显著降低。根、下胚轴和子叶表皮细胞中的肌动蛋白丝更短、更细，排列方向更随机，而肌动蛋白束更短，排列方向也发生了改变。der1-3 突变体中波浪状的根生长模式与根细胞中分裂平面（CDP）移位频率较高有关，这与微管为基础的前期带和纺锤体的移位定位一致。然而，der1-3 突变体根细胞中的皮质微管组织没有改变。
der1-3 突变体的根生长速度没有降低，但肌动蛋白细胞骨架组织的变化可以通过 CDP 方向的失调诱导波浪状的根生长模式。结果表明，ACT2 基因的 der1-3 突变不仅影响根毛形成过程，而且对肌动蛋白细胞骨架、植物生长和发育也有更普遍的影响。
