Buschmann Henrik, Hauptmann Monika, Niessing Dierk, Lloyd Clive W, Schäffner Anton R
Institute of Biochemical Plant Pathology, Helmholtz Zentrum München, 85764 Neuherberg, Germany.
Plant Cell. 2009 Jul;21(7):2090-106. doi: 10.1105/tpc.108.061242. Epub 2009 Jul 28.
Several factors regulate plant organ growth polarity. tortifolia2 (tor2), a right-handed helical growth mutant, has a conservative replacement of Arg-2 with Lys in the alpha-tubulin 4 protein. Based on a published high-resolution (2.89 A) tubulin structure, we predict that Arg-2 of alpha-tubulin forms hydrogen bonds with the GTPase domain of beta-tubulin, and structural modeling suggests that these contacts are interrupted in tor2. Consistent with this, we found that microtubule dynamicity is reduced in the tor2 background. We investigated the developmental origin of the helical growth phenotype using tor2. One hypothesis predicts that cell division patterns cause helical organ growth in Arabidopsis thaliana mutants. However, cell division patterns of tor2 root tips appear normal. Experimental uncoupling of cell division and expansion suggests that helical organ growth is based on cell elongation defects only. Another hypothesis is that twisting is due to inequalities in expansion of epidermal and cortical tissues. However, freely growing leaf trichomes of tor2 mutants show right-handed twisting and cortical microtubules form left-handed helices as early as the unbranched stage of trichome development. Trichome twisting is inverted in double mutants with tor3, a left-handed mutant. Single tor2 suspension cells also exhibit handed twisting. Thus, twisting of tor2 mutant organs appears to be a higher-order expression of the helical expansion of individual cells.
多种因素调控植物器官生长极性。tortifolia2（tor2）是一种右手螺旋生长突变体，其α-微管蛋白4蛋白中的精氨酸-2被赖氨酸保守取代。基于已发表的高分辨率（2.89 Å）微管蛋白结构，我们预测α-微管蛋白的精氨酸-2与β-微管蛋白的GTPase结构域形成氢键，并且结构建模表明这些接触在tor2中被中断。与此一致，我们发现tor2背景下微管动态性降低。我们使用tor2研究了螺旋生长表型的发育起源。一种假设预测细胞分裂模式导致拟南芥突变体中的螺旋器官生长。然而，tor2根尖的细胞分裂模式看起来正常。细胞分裂与扩展的实验解偶联表明螺旋器官生长仅基于细胞伸长缺陷。另一种假设是扭曲是由于表皮和皮层组织扩展不均。然而，tor2突变体自由生长的叶毛状体表现出右手扭曲，并且皮层微管在毛状体发育的未分支阶段就最早形成左手螺旋。在与左手突变体tor3的双突变体中，毛状体扭曲方向相反。单个tor2悬浮细胞也表现出特定方向的扭曲。因此，tor2突变体器官的扭曲似乎是单个细胞螺旋扩展的高阶表达。
