Legay Sylvain, Cocco Emmanuelle, André Christelle M, Guignard Cédric, Hausman Jean-Francois, Guerriero Gea
Luxembourg Institute of Science and Technology, Belvaux, Luxembourg.
Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
Front Plant Sci. 2017 Sep 26;8:1656. doi: 10.3389/fpls.2017.01656. eCollection 2017.
Russeting is characterized by a particular rough and brown phenotype, which is mainly due to the accumulation of suberin in the inner part of the epidermal cell walls. In our previous bulk transcriptomic analysis, comparing fully russeted, and waxy apple varieties, showed, in apple fruit skin, a massive decreased expression of cutin, wax and some pentacyclic triterpene biosynthesis genes in the russeted varieties, with an expected concomitant enhanced expression of the suberin biosynthetic genes. In the present work, we performed a deep investigation of the aliphatic composition of the cutin, suberin, waxes, and triterpenes in the waxy and russeted patches of the semi-russeted apple variety "Cox Orange Pippin." A targeted gene expression profiling was performed to validate candidate genes which were identified in our previous work and might be involved in the respective metabolic pathways. Our results showed that a decrease of cuticular waxes, ursolic acid and oleanolic acid, accompanied by an accumulation of alkyl-hydroxycinamates and betulinic acid, occurs in the russeted patches. The suberin monomer composition is characterized by specific occurrence of 20, 22, and 24 carbon aliphatic chains, whereas cutin is mainly represented by common C16 and C18 aliphatic chains. This work depicts, for the first time in apple, the complex composition of suberin, cutin, waxes and triterpenes, and confirms the strong interplay between these epidermal polymers in apple fruit skin.
果锈的特征是具有特定的粗糙褐色表型，这主要是由于表皮细胞壁内部木栓质的积累所致。在我们之前的大量转录组分析中，比较完全有锈斑的苹果品种和蜡质苹果品种发现，在苹果果皮中，有锈斑的品种中角质、蜡质和一些五环三萜生物合成基因的表达大幅下降，同时木栓质生物合成基因的表达相应增强。在本研究中，我们对半有锈斑的苹果品种“考克斯橙平皮”的蜡质区和有锈斑区的角质、木栓质、蜡质和三萜的脂肪族成分进行了深入研究。进行了靶向基因表达谱分析，以验证我们之前工作中鉴定出的可能参与各自代谢途径的候选基因。我们的结果表明，在有锈斑的区域，表皮蜡质、熊果酸和齐墩果酸减少，同时烷基羟基肉桂酸酯和桦木酸积累。木栓质单体组成的特征是特定出现20、22和24个碳的脂肪族链，而角质主要由常见的C16和C18脂肪族链代表。这项工作首次描绘了苹果中木栓质、角质、蜡质和三萜的复杂组成，并证实了这些表皮聚合物在苹果果皮中的强烈相互作用。
