Key Laboratory of Protected Horticulture of Education Ministry and Liaoning Province, National & Local Joint Engineering Research Center of Northern Horticultural, Facilities Design & Application Technology (Liaoning), College of Horticulture, Shenyang Agricultural University, Shenyang, 110866, Liaoning, People's Republic of China.
College of Ecology and Garden Architecture, Dezhou University, Dezhou, 253023, People's Republic of China.
Plant Mol Biol. 2020 Aug;103(6):689-704. doi: 10.1007/s11103-020-01018-7. Epub 2020 May 29.
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. 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.
CmCAD2 和 CmCAD3 在东方甜瓜中比 CmCAD1 更积极地促进木质素合成，这对于确保内部水分状态从而提高耐旱性很重要。木质素的良好形成可能是东方甜瓜耐旱时有效轴向水分运输和阻止侧向水分流动的保证，但仍有待验证。作为木质素合成途径中单宁醇脱氢酶（CAD）的重要酶，干旱通常会诱导甜瓜幼苗中五个肉桂醇脱氢酶（CAD）基因的表达。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 CAD 活性、木质素合成和组成，而 CmCAD1 的作用则较为温和。在甜瓜幼苗中，单独或集体沉默 CmCAD2 和 3 会大大降低 CAD 活性和木质素沉积，导致植株矮小。木质素的减少主要由 CmCAD3 催化的愈创木基单元组成，主要是由于木质部导管的木质化有限和 Casparion 带的发育。而 CmCAD1 和 2 分别对对香豆醛和芥子醛表现出催化作用。与 CmCAD1 相比，干旱处理显示出沉默甜瓜幼苗中 CmCAD2 和/或 3 的更高敏感性，伴随着相对较低的相对含水量、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加上有限的木质素化可能意味着沉默系茎部的侧向水分损失较高。在拟南芥中，CmCAD2 和 3 转基因系通过恢复木质素合成和根系发育来增强 cadc cadd 的耐旱性，伴随着电解质泄漏比例的降低和 RWCs 的增加，从而提高了存活率。简而言之，CmCAD2 和 3 合成的木质素在甜瓜的耐旱性中起着重要作用。
