An Endosperm-Associated Cuticle Is Required for Arabidopsis Seed Viability, Dormancy and Early Control of Germination.
An Endosperm-Associated Cuticle Is Required for Arabidopsis Seed Viability, Dormancy and Early Control of Germination.
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DOI：
10.1371/journal.pgen.1005708
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发表时间：
2015-12
期刊：
影响因子：
4.5
通讯作者：
Lopez-Molina L
中科院分区：
文献类型：
--
作者：
De Giorgi J;Piskurewicz U;Loubery S;Utz-Pugin A;Bailly C;Mène-Saffrané L;Lopez-Molina L
角质层和种子是植物对陆生生活的重要适应，它们分别出现在植物进化的早期和晚期。角质层是覆盖植物气生器官的防水膜，防止水分过度流失，并保护植物免受生物和非生物胁迫。由交联脂肪酸单体组成的角质层是最丰富和研究最多的表皮成分。种子是干燥的，代谢惰性的结构，通过保持植物胚处于被逮捕的保护状态来促进植物传播。在拟南芥种子中，胚被单细胞胚乳层包围，胚乳层本身被种皮层包围。全基因组分析导致我们确定角质生物合成基因的调控目标的植物激素赤霉素（GA）和脱落酸（阿坝）的信号通路，控制种子萌发。角质层存在于许多物种的种皮中，包括拟南芥，它们调节对外部化合物的渗透性。然而，角质在成熟种子生理和萌发中的作用仍然知之甚少。在这里，我们确定在成熟的种子厚角质膜覆盖整个外表面的胚乳。这种种子角质层是有缺陷的角质缺乏bodyguard 1种子，这是与胚乳渗透性的改变。此外，角质生物合成受影响的突变体显示低种子休眠和生活力水平，这与较高水平的种子脂质氧化应激相关。种子吸胀后，角质合成基因是防止胚乳细胞膨胀和种皮破裂所必需的。总之，我们的研究结果表明，在陆地植物进化的过程中，角质层结构被增选，以实现关键的生理种子特性。种子是陆地植物进化过程中出现较晚的重要结构。事实上，在种子中，植物胚处于代谢惰性和高度抗性状态。种子使植物得以分散并找到有利的生存环境。同样值得注意的是，“濒临死亡”的胚胎能够发芽，变成脆弱的幼苗。这一转变的脆弱性暴露于控制机制的存在，这种机制会阻止发芽，以应对有害的环境条件。因此，种子将植物转化为时间和空间旅行者，并在很大程度上解释了开花植物对陆地植物的殖民。这一成功的关键在于种子的生理功能，这是植物生物学中一个尚未解决的重大问题。我们发现，模式植物拟南芥的成熟种子包含一个早期的陆地植物进化创新：角质层，一个蜡质薄膜覆盖在植物的空中部分，防止过度蒸腾。种子角质层包含角质（叶角质层的主要脂质聚合物组分），将种子内的所有活组织包围起来。具有角质缺陷的种子被高度氧化，并且具有低的种子生活力和休眠。它们也无法控制自己的发芽。因此，陆地植物选择了一项古老的创新，以实现种子的卓越生理功能。
Cuticular layers and seeds are prominent plant adaptations to terrestrial life that appeared early and late during plant evolution, respectively. The cuticle is a waterproof film covering plant aerial organs preventing excessive water loss and protecting against biotic and abiotic stresses. Cutin, consisting of crosslinked fatty acid monomers, is the most abundant and studied cuticular component. Seeds are dry, metabolically inert structures promoting plant dispersal by keeping the plant embryo in an arrested protected state. In Arabidopsis thaliana seeds, the embryo is surrounded by a single cell endosperm layer itself surrounded by a seed coat layer, the testa. Whole genome analyses lead us to identify cutin biosynthesis genes as regulatory targets of the phytohormones gibberellins (GA) and abscisic acid (ABA) signaling pathways that control seed germination. Cutin-containing layers are present in seed coats of numerous species, including Arabidopsis, where they regulate permeability to outer compounds. However, the role of cutin in mature seed physiology and germination remains poorly understood. Here we identify in mature seeds a thick cuticular film covering the entire outer surface of the endosperm. This seed cuticle is defective in cutin-deficient bodyguard1 seeds, which is associated with alterations in endospermic permeability. Furthermore, mutants affected in cutin biosynthesis display low seed dormancy and viability levels, which correlates with higher levels of seed lipid oxidative stress. Upon seed imbibition cutin biosynthesis genes are essential to prevent endosperm cellular expansion and testa rupture in response to low GA synthesis. Taken together, our findings suggest that in the course of land plant evolution cuticular structures were co-opted to achieve key physiological seed properties. Seeds are remarkable plant structures that appeared late during land plant evolution. Indeed, within seeds plant embryos lie in a metabolic inert and highly resistant state. Seeds allow plants to disperse and find a favorable living environment. Remarkably as well, the “near-dead” embryo is able to germinate and turn into a fragile young seedling. The fragility of this transition is betrayed by the existence of control mechanisms that block germination in response to harmful environmental conditions. Seeds therefore transform plants into time and space travellers and largely explain land plant colonization by flowering plants. The key to this success lies in the seed’s physiological feats, a major yet unresolved question in plant biology. We show that mature seeds of the model plant Arabidopsis contain an earlier land plant evolutionary innovation: the cuticle, a waxy film covering the aerial parts of the plant preventing excessive transpiration. The seed cuticle, which contains cutin, a major lipid polymer component of the leaf cuticle, encloses all the living tissues within the seed. Seeds with cutin defects are highly oxidized and have low seed viability and dormancy. They are also unable to control their germination. Thus, land plants co-opted an ancient innovation to achieve the remarkable physiology of seeds.