Yu L M
Center for Engineering Plants for Resistance Against Pathogens (CEPRAP), University of California, Davis 95616, USA.
Proc Natl Acad Sci U S A. 1995 May 9;92(10):4088-94. doi: 10.1073/pnas.92.10.4088.
Elicitins are a family of small proteins secreted by species of Phytophthora. They are thought to be major determinants of the resistance response of tobacco against these oomycetes, since purified elicitins, alone and at low concentrations, can induce vigorous defense responses in tobacco (i.e., hypersensitive cell death and resistance against subsequent pathogen attack), and in vitro elicitin production by Phytophthora isolates is strongly negatively correlated with their pathogenicity on tobacco plants. A number of elicitins have been purified and their amino acid sequences have been determined and found to be conserved. A three-dimensional structure for elicitin is emerging from nuclear magnetic resonance studies. Two structural classes, alpha and beta, are distinguished by their biological effects when applied to decapitated stems or petioles; the beta class causes more necrosis on leaves and provides better subsequent protection against pathogen attack. However, both these classes of elicitins will similarly cause necrosis when each is, instead, directly infiltrated into tobacco leaf panels. Effects of elicitins on tobacco cells include rapid electrolyte leakage, changes in protein phosphorylation and amounts of active oxygen species, and later production of ethylene and capsidiol. The sites of initial interaction with tobacco cells are unknown, but the interaction appears to induce general defense-related responses.
激发素是由疫霉属物种分泌的一类小蛋白。它们被认为是烟草对这些卵菌抗性反应的主要决定因素，因为纯化的激发素单独使用且浓度较低时，就能在烟草中诱导强烈的防御反应（即超敏细胞死亡以及对后续病原体攻击的抗性），而且疫霉分离株在体外产生激发素的能力与其对烟草植株的致病性呈强烈负相关。多种激发素已被纯化，其氨基酸序列也已确定，并且发现这些序列具有保守性。通过核磁共振研究，激发素的三维结构正在显现。根据应用于去顶茎或叶柄时的生物学效应，可区分出α和β两种结构类型；β型在叶片上会引起更多坏死，并能为后续抵御病原体攻击提供更好的保护。然而，当将这两类激发素直接注射到烟草叶片组织中时，它们都会同样地引起坏死。激发素对烟草细胞的影响包括电解质快速渗漏、蛋白质磷酸化和活性氧含量的变化，以及随后乙烯和辣椒二醇的产生。与烟草细胞最初相互作用的位点尚不清楚，但这种相互作用似乎会诱导一般的防御相关反应。
