Hein John W, Wolfe Gordon V, Blee Kristopher A
Department of Biological Sciences, California State University, Chico, CA 95929-0515, USA.
Microb Ecol. 2008 Feb;55(2):333-43. doi: 10.1007/s00248-007-9279-1. Epub 2007 Jul 7.
Systemic acquired resistance (SAR) is an inducible systemic plant defense against a broad spectrum of plant pathogens, with the potential to secrete antimicrobial compounds into the soil. However, its impact on rhizosphere bacteria is not known. In this study, we examined fingerprints of bacterial communities in the rhizosphere of the model plant Arabidopsis thaliana to determine the effect of SAR on bacterial community structure and diversity. We compared Arabidopsis mutants that are constitutive and non-inducible for SAR and verified SAR activation by measuring pathogenesis-related protein activity via a beta-glucoronidase (GUS) reporter construct driven by the beta-1-3 glucanase promoter. We used terminal restriction fragment length polymorphism (T-RFLP) analysis of MspI- and HaeIII-digested 16S rDNA to estimate bacterial rhizosphere community diversity, with Lactobacillus sp. added as internal controls. T-RFLP analysis showed a clear rhizosphere effect on community structure, and diversity analysis of both rhizosphere and bulk soil operational taxonomic units (as defined by terminal restriction fragments) using richness, Shannon-Weiner, and Simpson's diversity indices and evenness confirmed that the presence of Arabidopsis roots significantly altered bacterial communities. This effect of altered soil microbial community structure by plants was also seen upon multivariate cluster analysis of the terminal restriction fragments. We also found visible differences in the rhizosphere community fingerprints of different Arabidopsis SAR mutants; however, there was no clear decrease of rhizosphere diversity because of constitutive SAR expression. Our study suggests that SAR can alter rhizosphere bacterial communities, opening the door to further understanding and application of inducible plant defense as a driving force in structuring soil bacterial assemblages.
系统获得性抗性（SAR）是植物针对多种植物病原体的一种可诱导的系统性防御机制，具有向土壤中分泌抗菌化合物的潜力。然而，其对根际细菌的影响尚不清楚。在本研究中，我们检测了模式植物拟南芥根际细菌群落的指纹图谱，以确定系统获得性抗性对细菌群落结构和多样性的影响。我们比较了组成型和非诱导型系统获得性抗性的拟南芥突变体，并通过由β-1,3-葡聚糖酶启动子驱动的β-葡萄糖醛酸酶（GUS）报告构建体测量病程相关蛋白活性来验证系统获得性抗性的激活。我们使用对MspI和HaeIII消化的16S rDNA进行末端限制性片段长度多态性（T-RFLP）分析来估计根际细菌群落多样性，并添加乳酸杆菌作为内部对照。T-RFLP分析显示根际对群落结构有明显影响，使用丰富度、香农-维纳和辛普森多样性指数以及均匀度对根际和根际外土壤操作分类单元（由末端限制性片段定义）进行多样性分析，证实拟南芥根的存在显著改变了细菌群落。在对末端限制性片段进行多变量聚类分析时，也发现了植物对土壤微生物群落结构改变的这种影响。我们还发现不同拟南芥系统获得性抗性突变体的根际群落指纹图谱存在明显差异；然而，由于组成型系统获得性抗性表达，根际多样性并没有明显降低。我们的研究表明，系统获得性抗性可以改变根际细菌群落，为进一步理解和应用可诱导植物防御作为构建土壤细菌组合的驱动力打开了大门。
