Duke Kelly A, Becker Michael G, Girard Ian J, Millar Jenna L, Dilantha Fernando W G, Belmonte Mark F, de Kievit Teresa R
Department of Microbiology, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
Department of Biological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
BMC Genomics. 2017 Jun 19;18(1):467. doi: 10.1186/s12864-017-3848-6.
The biological control agent Pseudomonas chlororaphis PA23 is capable of protecting Brassica napus (canola) from the necrotrophic fungus Sclerotinia sclerotiorum via direct antagonism. While we have elucidated bacterial genes and gene products responsible biocontrol, little is known about how the host plant responds to bacterial priming on the leaf surface, including global changes in gene activity in the presence and absence of S. sclerotiorum.
Application of PA23 to the aerial surfaces of canola plants reduced the number of S. sclerotiorum lesion-forming petals by 91.1%. RNA sequencing of the host pathogen interface showed that pretreatment with PA23 reduced the number of genes upregulated in response to S. sclerotiorum by 16-fold. By itself, PA23 activated unique defense networks indicative of defense priming. Genes encoding MAMP-triggered immunity receptors detecting flagellin and peptidoglycan were downregulated in PA23 only-treated plants, consistent with post-stimulus desensitization. Downstream, we observed reactive oxygen species (ROS) production involving low levels of HO and overexpression of genes associated with glycerol-3-phosphate (G3P)-mediated systemic acquired resistance (SAR). Leaf chloroplasts exhibited increased thylakoid membrane structures and chlorophyll content, while lipid metabolic processes were upregulated.
In addition to directly antagonizing S. sclerotiorum, PA23 primes the plant defense response through induction of unique local and systemic defense networks. This study provides novel insight into the effects of biocontrol agents applied to the plant phyllosphere. Understanding these interactions will aid in the development of biocontrol systems as an alternative to chemical pesticides for protection of important crop systems.
生防菌绿针假单胞菌PA23能够通过直接拮抗作用保护甘蓝型油菜（油菜）免受坏死营养型真菌核盘菌的侵害。虽然我们已经阐明了负责生物防治的细菌基因和基因产物，但对于宿主植物如何响应叶表面的细菌引发作用，包括在有和没有核盘菌的情况下基因活性的整体变化，我们了解得很少。
将PA23施用于油菜植株的地上部分，可使形成核盘菌病斑的花瓣数量减少91.1%。宿主-病原体界面的RNA测序表明，用PA23预处理可使响应核盘菌而上调的基因数量减少16倍。PA23本身激活了指示防御引发的独特防御网络。在仅用PA23处理的植物中，编码检测鞭毛蛋白和肽聚糖的MAMP触发免疫受体的基因被下调，这与刺激后脱敏一致。在下游，我们观察到活性氧（ROS）的产生，涉及低水平的HO以及与甘油-3-磷酸（G3P）介导的系统获得性抗性（SAR）相关基因的过表达。叶片叶绿体的类囊体膜结构增加，叶绿素含量增加，同时脂质代谢过程上调。
除了直接拮抗核盘菌外，PA23还通过诱导独特的局部和系统防御网络来引发植物防御反应。本研究为应用于植物叶际的生防菌的作用提供了新的见解。了解这些相互作用将有助于开发生物防治系统，作为保护重要作物系统的化学农药的替代品。
