Department of Agrobiology and Agrochemistry, University of Tuscia, Viterbo, Italy.
Mol Plant Microbe Interact. 2011 Sep;24(9):1012-9. doi: 10.1094/MPMI-01-11-0021.
Cell wall pectin methyl esterification can influence plant resistance because highly methyl-esterified pectin can be less susceptible to the hydrolysis by pectic enzymes such as fungal endopolygalacturonases (PG). Pectin is secreted into the cell wall in a highly methyl-esterified form and, here, is de-methyl esterified by pectin methyl esterase (PME). The activity of PME is controlled by specific protein inhibitors called PMEI; consequently, an increased inhibition of PME by PMEI might modify the pectin methyl esterification. In order to test the possibility of improving wheat resistance by modifying the methyl esterification of pectin cell wall, we have produced durum wheat transgenic lines expressing the PMEI from Actinidia chinensis (AcPMEI). The expression of AcPMEI endows wheat with a reduced endogenous PME activity, and transgenic lines expressing a high level of the inhibitor showed a significant increase in the degree of methyl esterification. These lines showed a significant reduction of disease symptoms caused by the fungal pathogens Bipolaris sorokiniana or Fusarium graminearum. This increased resistance was related to the impaired ability of these fungal pathogens to grow on methyl-esterified pectin and to a reduced activity of the fungal PG to hydrolyze methyl-esterified pectin. In addition to their importance for wheat improvement, these results highlight the primary role of pectin despite its low content in the wheat cell wall.
细胞壁果胶甲酯化可以影响植物的抗性，因为高度甲酯化的果胶可能不易被果胶酶如真菌内切多聚半乳糖醛酸酶（PG）水解。果胶以高度甲酯化的形式分泌到细胞壁中，并在此处被果胶甲酯酶（PME）去甲酯化。PME 的活性受到称为 PMEI 的特定蛋白质抑制剂的控制；因此，PMEI 对 PME 的抑制增加可能会改变果胶的甲酯化。为了测试通过修饰果胶细胞壁的甲酯化来提高小麦抗性的可能性，我们已经生产了表达猕猴桃 PMEI（AcPMEI）的硬粒小麦转基因系。AcPMEI 的表达赋予小麦降低的内源性 PME 活性，并且表达高水平抑制剂的转基因系表现出显著增加的甲酯化程度。这些系表现出真菌病原体双极镰刀菌或禾谷镰刀菌引起的症状显著减少。这种增加的抗性与这些真菌病原体在甲酯化果胶上生长的能力受损以及真菌 PG 水解甲酯化果胶的活性降低有关。除了对小麦改良的重要性外，这些结果还强调了果胶在小麦细胞壁中含量低的情况下的主要作用。
