Water transportation to developing tissues relies on the structure and function of plant xylem cells. Plant microtubules govern the direction of cellulose microfibrils and guide secondary cell wall formation and morphogenesis. However, the relevance of microtubule-determined xylem wall thickening patterns in plant hydraulic conductivity remains unclear. In the present study, we identified a maize (Zea mays) semi-dominant mutant, designated drought-overly-sensitive1 (ZmDos1), the upper leaves of which wilted even when exposed to well-watered conditions during growth; the wilting phenotype was aggravated by increased temperatures and decreased humidity. Protoxylem vessels in the stem and leaves of the mutant showed altered thickening patterns of the secondary cell wall (from annular to spiral), decreased inner diameters, and limited water transport efficiency. The causal mutation for this phenotype was found to be a G-to-A mutation in the maize gene α-tubulin4, resulting in a single amino acid substitution at position 196 (E196K). Ectopic expression of the mutant α-tubulin4 in Arabidopsis (Arabidopsis thaliana) changed the orientation of microtubule arrays, suggesting a determinant role of this gene in microtubule assembly and secondary cell wall thickening. Our findings suggest that the spiral wall thickenings triggered by the α-tubulin mutation are stretched during organ elongation, causing a smaller inner diameter of the protoxylem vessels and affecting water transport in maize. This study underscores the importance of tubulin-mediated protoxylem wall thickening in regulating plant hydraulics, improves our understanding of the relationships between protoxylem structural features and functions, and offers candidate genes for the genetic enhancement of maize.

中文翻译：

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微管蛋白参与建立玉米中的原木质部血管增强模式和水力传导性


水向发育组织的运输依赖于植物木质部细胞的结构和功能。植物微管控制纤维素微纤维的方向并指导次生细胞壁的形成和形态发生。然而，微管决定的木质部壁增厚模式与植物水力传导率的相关性仍不清楚。在本研究中，我们鉴定了一种玉米（Zea mays）半显性突变体，命名为干旱过度敏感1（ZmDos1），即使在生长过程中暴露于水分充足的条件下，其上部叶片也会枯萎；温度升高和湿度降低加剧了枯萎表型。突变体茎和叶中的原木质部导管显示出次生细胞壁增厚模式的改变（从环形到螺旋）、内径减小和水运输效率有限。发现该表型的致病突变是玉米基因 α-微管蛋白4 中的 G 到 A 突变，导致 196 位 (E196K) 处出现单个氨基酸取代。拟南芥中突变体 α-tubulin4 的异位表达改变了微管阵列的方向，表明该基因在微管组装和次生细胞壁增厚中起决定性作用。我们的研究结果表明，α-微管蛋白突变引发的螺旋壁增厚在器官伸长过程中被拉伸，导致原木质部血管内径变小并影响玉米中的水分运输。这项研究强调了微管蛋白介导的原木质部壁增厚在调节植物水力学中的重要性，提高了我们对原木质部结构特征和功能之间关系的理解，并为玉米遗传增强提供了候选基因。