Conn V M, Walker A R, Franco C M M
Department of Medical Biotechnology, Flinders University, Bedford Park, South Australia 5042, Australia.
Mol Plant Microbe Interact. 2008 Feb;21(2):208-18. doi: 10.1094/MPMI-21-2-0208.
Endophytic actinobacteria, isolated from healthy wheat tissue, which are capable of suppressing a number wheat fungal pathogens both in vitro and in planta, were investigated for the ability to activate key genes in the systemic acquired resistance (SAR) or the jasmonate/ethylene (JA/ET) pathways in Arabidopsis thaliana. Inoculation of A. thaliana (Col-0) with selected endophytic strains induced a low level of SAR and JA/ET gene expression, measured using quantitative polymerase chain reaction. Upon pathogen challenge, endophyte-treated plants demonstrated a higher abundance of defense gene expression compared with the non-endophyte-treated controls. Resistance to the bacterial pathogen Erwinia carotovora subsp. carotovora required the JA/ET pathway. On the other hand, resistance to the fungal pathogen Fusarium oxysporum involved primarily the SAR pathway. The endophytic actinobacteria appear to be able to "prime" both the SAR and JA/ET pathways, upregulating genes in either pathway depending on the infecting pathogen. Culture filtrates of the endophytic actinobacteria were investigated for the ability to also activate defense pathways. The culture filtrate of Micromonospora sp. strain EN43 grown in a minimal medium resulted in the induction of the SAR pathway; however, when grown in a complex medium, the JA/ET pathway was activated. Further analysis using Streptomyces sp. strain EN27 and defense-compromised mutants of A. thaliana indicated that resistance to E. carotovora subsp. carotovora occurred via an NPR1-independent pathway and required salicylic acid whereas the JA/ET signaling molecules were not essential. In contrast, resistance to F. oxysporum mediated by Streptomyces sp. strain EN27 occurred via an NPR1-dependent pathway but also required salicylic acid and was JA/ET independent.
从健康小麦组织中分离出的内生放线菌能够在体外和植物体内抑制多种小麦真菌病原体，本研究对其激活拟南芥系统获得性抗性（SAR）或茉莉酸/乙烯（JA/ET）途径中关键基因的能力进行了探究。用定量聚合酶链反应检测发现，用选定的内生菌株接种拟南芥（Col-0）可诱导低水平的SAR和JA/ET基因表达。在病原体攻击后，与未用内生菌处理的对照相比，经内生菌处理的植物表现出更高丰度的防御基因表达。对细菌性病原体胡萝卜软腐欧文氏菌胡萝卜软腐亚种的抗性需要JA/ET途径。另一方面，对真菌病原体尖孢镰刀菌的抗性主要涉及SAR途径。内生放线菌似乎能够“启动”SAR和JA/ET途径，根据感染的病原体上调任一途径中的基因。对内生放线菌的培养滤液激活防御途径的能力也进行了研究。在基本培养基中生长的小单孢菌属菌株EN43的培养滤液可诱导SAR途径；然而，在复杂培养基中生长时，JA/ET途径被激活。使用链霉菌属菌株EN27和拟南芥防御缺陷型突变体的进一步分析表明，对胡萝卜软腐欧文氏菌胡萝卜软腐亚种的抗性通过不依赖NPR1的途径发生，需要水杨酸，而JA/ET信号分子并非必需。相比之下，链霉菌属菌株EN27介导的对尖孢镰刀菌的抗性通过依赖NPR1的途径发生，但也需要水杨酸，且不依赖JA/ET。
