State Key Laboratory of Conservation and Utilization of Subtropical Agro-bioresources, Guangdong Province Key Laboratory of Microbial Signals and Disease Control, College of Agriculture, South China Agricultural University, Guangzhou, 510642, China.
College of Horticulture, South China Agricultural University, Guangzhou, 510642, China.
Sci Rep. 2017 Oct 13;7(1):13140. doi: 10.1038/s41598-017-13625-4.
Plant cell walls, which are mainly composed of pectin, play important roles in plant defence responses to pathogens. Pectin is synthesised in a highly esterified form and then de-esterified by pectin methylesterases (PMEs). Because of this, PMEs are directly involved in plant defence. However, the molecular mechanisms of their interactions with pectins remain unclear. In this study, we compared the expression level and enzyme activities of PMEs in a banana Cavendish cultivar (Musa AAA 'Brazilian') inoculated with Fusarium oxysporum f. sp. cubense pathogenic races 1 (Foc1) and 4 (Foc4). We further examined the spatial distribution of PMEs and five individual homogalacturonans (HGs) with different degree of pectin methylesterification (DM). Results suggested that the banana roots infected with Foc1 showed lower PME activity than those infected with Foc4, which was consisted with observed higher level of pectin DM. The level of HGs crosslinked with Ca was significantly higher in roots infected with Foc1 compared with those infected with Foc4. Therefore, banana exhibited significantly different responses to Foc1 and Foc4 infection, and these results suggest differences in PME activities, DM of pectin and Ca-bridged HG production. These differences could have resulted in observed differences in virulence between Foc1 and Foc4.
植物细胞壁主要由果胶组成，在植物对病原体的防御反应中起着重要作用。果胶以高度酯化的形式合成，然后被果胶甲酯酶（PMEs）去酯化。正因为如此，PMEs直接参与植物防御。然而，它们与果胶相互作用的分子机制仍不清楚。在这项研究中，我们比较了接种尖孢镰刀菌古巴专化型 1 号（Foc1）和 4 号（Foc4）致病小种的巴西蕉（Musa AAA '巴西'）中 PME 的表达水平和酶活性。我们进一步研究了 PME 和五种具有不同程度果胶甲酯化（DM）的单体同质半乳糖醛酸聚糖（HG）的空间分布。结果表明，感染 Foc1 的香蕉根中的 PME 活性低于感染 Foc4 的，这与观察到的较高的果胶 DM 水平一致。与感染 Foc4 的相比，感染 Foc1 的香蕉根中与 Ca 交联的 HG 水平显著升高。因此，香蕉对 Foc1 和 Foc4 的感染表现出明显不同的反应，这些结果表明 PME 活性、果胶 DM 和 Ca 桥接 HG 产生的差异。这些差异可能导致 Foc1 和 Foc4 之间毒力的差异。
