Key message

CmCAD2 and CmCAD3 function more positively than CmCAD1 in oriental melon for lignin synthesis which is important to ensure internal water status and thus for drought tolerance.

Abstract

Well-lignification may be the guarantee of efficient axial water transport and barrier of lateral water flow in oriental melon tolerating drought stress, however remains to be verified. As an important enzyme in monolignol synthesis pathway, five cinnamyl alcohol dehydrogenase (CAD) genes were generally induced in melon seedlings by drought. Here we further revealed the roles of CmCAD1, 2, and 3 in lignin synthesis and for drought tolerance. Results found that overexpressing CmCAD2 or 3 strongly recovered CAD activities, lignin synthesis and composition in Arabidopsis cadc cadd, whose lignin synthesis is disrupted, while CmCAD1 functioned modestly. In melon seedlings, silenced CmCAD2 and 3 individually or collectively decreased CAD activities and lignin depositions drastically, resulting in dwarfed phenotypes. Reduced lignin, mainly composed by guaiacyl units catalyzed by CmCAD3, is mainly due to the limited lignification in tracheary elements and development of Casparion strip. While CmCAD1 and 2 exhibited catalysis to p-coumaraldehyde and sinapaldehyde, respectively. Compared with CmCAD1, drought treatments revealed higher sensitivity of CmCAD2 and/or 3 silenced melon seedlings, accompanying with lower relative water contents, water potentials and relatively higher total soluble sugar contents. Slightly up-regulated expressions of aquaporin genes together with limited lignification might imply higher lateral water loss in stems of silenced lines. In Arabidopsis, CmCAD2 and 3 transgenic lines enhanced cadc cadd drought tolerance through recovering lignin synthesis and root development, accompanying with decreased electrolyte leakage ratios and increased RWCs, thus improved survival rates. Briefly, lignin synthesized by CmCAD2 and 3 functions importantly for drought tolerance in melon.

中文翻译：

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由 CmCAD2 和 CmCAD3 在香瓜 (Cucumis melo L.) 幼苗中合成的木质素有助于提高耐旱性。

关键信息

CmCAD2和CmCAD3在西瓜中对木质素合成的作用比CmCAD1更积极，这对于确保内部水分状况和耐旱性很重要。

抽象的

木质化可能是冬瓜耐受干旱胁迫时轴向水分高效输送和侧向水流屏障的保证，但仍有待验证。5个肉桂醇脱氢酶(CAD)基因作为木酚醇合成途径中的重要酶，在甜瓜幼苗中普遍受到干旱诱导。在这里，我们进一步揭示了CmCAD1、2和3在木质素合成和耐旱性中的作用。结果发现，过表达CmCAD2或3强烈恢复了拟南芥cadc cadd中的CAD 活性、木质素合成和组成，其木质素合成被破坏，而CmCAD1适度发挥作用。在瓜苗中，沉默的 CmCAD2和3单独或共同降低 CAD 活性和木质素沉积，导致表型矮化。还原的木质素主要由 CmCAD3 催化的愈创木酰基单元组成，主要是由于气管元素的有限木质化和 Casparion 条的发育。而 CmCAD1 和 2 分别表现出对对香豆醛和芥子醛的催化作用。与CmCAD1相比，干旱处理对CmCAD2和/或3的敏感性更高沉默的甜瓜幼苗，伴随着较低的相对含水量、水势和相对较高的总可溶性糖含量。水通道蛋白基因的轻微上调表达以及有限的木质化可能意味着沉默系茎的侧向失水量更高。在拟南芥中，CmCAD2和3转基因品系通过恢复木质素合成和根系发育来增强cadc cadd耐旱性，同时降低电解质泄漏率和增加 RWC，从而提高存活率。简而言之，由CmCAD2和3合成的木质素对甜瓜的耐旱性具有重要作用。