激发素与植物互作及抗病防卫信号传导

Elicitin-plant interaction and signal transduction of defense reaction

激发素是一类由疫霉属 Phytophthora 等真菌分泌的,可诱导茄科、十字花科等植物过敏性反应和系统获得抗病性的蛋白类激发子。激发素与植物的互作系统为研究植物抗病防卫信号传导途径提供了一个极好的模式。最近发现:激发素具有转移甾醇的活性,而形成甾醇和激发素复合物又是激发素与受体蛋白互作和激活抗病防卫信号传导途径的前提条件,也是对最近提出的病原激发子与受体互作“保卫假说”的支持。用^(125)I 标记法,找到了激发素的受体蛋白,由分子量约为160kD 和50kD 的2个亚基构成,被认为是 Ca^(2+)通道。在激发素激活的烟草抗病防卫信号传导途径中,蛋白质的磷酸化起着至关重要的作用,抑制蛋白激酶的活性,可阻止离子交换、活性氧进发、植保素合成等多种防卫反应;Ca^(2+)参与诱导活性氧进发和植保素合成,活性氧进发与细胞死亡相关连,而植保素的合成与活性氧进发无关,过敏性反应对抗病防卫反应的建立不是必需的。激发素抗病基因工程在广谱抗病育种中具有广泛的应用前景。

Elicitins,the small proteins secreted by Phytophthora and Pythium species,havebeen shown to induce a hypersensitive reaction and systemic acquired resistance in someplants.Moreover,these plants become resistant to their pathogens,and thus this interactionconstitutes an excellent model to investigate the signaling pathways leading to plant resistance.The recent discovery of the sterol carrier activity of elicitin brings a new insight on their molecu-lar activity.This constitutes a crucial property,since the formation of a sterol-elicitin complexis required to trigger the biological responses of tobacco cells and plants.Only the elicitinsloaded with a sterol are able to bind to their plasmalemma receptor,which is assumed to be anallosteric calcium channel,comprising two basal subunits(al60kD and 50kD).In the signaltransduction of defense reactions triggered by elicitins,protein phosphorylation was important,because inhibition of protein kinase activity caused the suppression of ion fluxed,the generationof AOS,and the synthesis of phytoalexins.Ca^(2+)played a significant role in induction of the ac-cumulation of phytoalexins and burst of AOS which related to cell death,but not to the synthe-sis of phytoalexins.The hypersensitive reaction does not seem to be essential for the establish-ment of SAR.Durability and effectiveness of elicitin-induced SAR toward a wide variety ofpathogens show that elicitins are powerful elicitors of long term and aspecific protection ofplants.