katG基因在豌豆根瘤菌抗氧化中的功能

Antioxidative function of katG gene in Rhizobium leguminosarum

摘要:

摘要:【目的】细菌中过氧化物/过氧化氢酶KatG参与活性氧(ROS)的解毒过程，从而防止其对细菌生长伤害，本文研究根瘤菌中katG基因的抗氧化功能对豌豆根瘤菌3841生长及共生固氮的影响。【方法】通过基因敲除、遗传互补和对菌株的抗氧化和共生能力分析，系统地探究了根瘤菌中katG基因的功能。【结果】katG基因突变不影响菌株在自生培养条件下生长状况，但H2O2短时间处理导致突变株的存活率显著下降。实时荧光定量RT-PCR结果显示，H2O2不能诱导豌豆根瘤菌3841katG基因的表达。进一步研究发现突变体中katG基因缺失能显著提高抗氧化基因ohrB的表达，而降低grxC基因的表达。植物盆栽实验发现，katG突变虽然对根瘤菌共生固氮能力和竞争结瘤能力均无影响，但katG在类菌体中表达显著下调。同时，katG突变显著影响了根瘤菌在植物根圈中的定殖能力。【结论】研究表明katG虽对豌豆根瘤菌自生和共生固氮无明显影响，但在抗氧化和根圈定殖中起重要作用，外源H2O2对katG的表达无诱导作用，但katG调节ohrB和grxC等抗氧化基因的表达，从而在抗氧化和共生中发挥作用。

Abstract:

Abstract:［Objective］Catalase-peroxidase KatG can protect bacteria from damage of reactive oxygen species．This study investigated the antioxidative function of catalase－peroxidase gene katG in Ｒhizobium leguminosarum 3841.［Methods］katG mutant strain of R.leguminosarum was constructed by homologous recombination．The wild type，katG mutant and complementary strain were challenged by oxidative stress and symbiotic ability.［Results］Under free－living conditions，the katG mutant exhibited no generation time extension． However，cells of the katG strain were deficient in consumption of high concentrations of H2O2 and were vulnerable after aquick exposure to H2O2. The real-time qRT-PCR results showed that katG was expressed independently of exogenous H2O2．In contrast，the katG mutant strain displayed higher express level of ohrB gene and lower expression level of grxC than the wild type． With regard to symbiotic capacities with Pisum sativum，the katG mutant was indistinguishable in root nodule nitrogenase activity and competition nodule ability from the wild type．However，katG gene was expressed significantly lower in bacteroids than that in free-living strains． Besides，the colonization of the pea rhizosphere by the katG mutant was impaired compared to that of the wild type.［Conclusion］The deletion of katG had nosignificant effect in 3841 under the free-living and symbiosis condition but was essential in antioxidation and colonization of the pea rhizosphere． Although katG could not be induced by H2O2，it still played acentral role in antioxidation and symbiotic nitrogen fixation by regulating the antioxidant genes such as ohrB and grxC.