Burkholderia sp. AU4i is a strain previously isolated from pea, which can act as plant growth-promoting rhizobacteria (PGPR). Here, we demonstrate that AU4i is able to promote Arabidopsis growth and increase the number of lateral roots as well as shoot and root dry weight. The inoculation of Arabidopsis leaves with AU4i significantly reduced the lesion’s areas provoked by the necrotrophic pathogens Botrytis cinerea and Sclerotinia sclerotiorum. Bacterial inoculation induced the expression of the jasmonate responsive marker gene AtPDF1.2, but not the expression of salicylic acid marker gene AtPR-1. Notwithstanding, similar AU4i protective effect was observed in Arabidopsis mutants coi1 and sid2-2 (defective in jasmonate perception and salicylic acid synthesis, respectively) compared with Col-0 plants. Thus, the independence of the AU4i protective effect and plant defence signalling pathways is suggested. AU4i inoculation was able to induced anthocyanins and phenolic compounds accumulation, as well as phenylalanine ammonia-lyase activity. Moreover, the effect of AU4i inoculation on the metabolism of plant cell wall was evaluated. As a result, B. cinerea and S. sclerotiorum mycelial growth was reduced in culture media containing cell wall polysaccharides from inoculated Arabidopsis leaves. Additionally, leaves colonized by AU4i showed the downregulation of genes involved in hemicelluloses and pectins degradation (AtExp8 and AtAra1, respectively) and the upregulation of AtPME3, a gene encoding a putative pectin methylesterase involved in pectin main chain de-esterification. Taken together, our results suggest Burkholderia sp. AU4i not only as potential biocontrol agent, but also as a good candidate for better understanding the mechanisms used by PGPRs to protect plants from fungal attacks.

中文翻译：

---

伯克霍尔德菌属 菌株 AU4i 促进拟南芥生长并增加植物对坏死性病原体的防御反应

伯克霍尔德菌属 AU4i 是一种先前从豌豆中分离出来的菌株，可作为植物生长促进根际细菌 (PGPR)。在这里，我们证明 AU4i 能够促进拟南芥生长并增加侧根数量以及芽和根干重。用 AU4i 接种拟南芥叶显着减少了由坏死性病原体灰葡萄孢和核盘菌引起的病灶面积。细菌接种诱导茉莉酸反应标记基因 AtPDF1.2 的表达，但不诱导水杨酸标记基因 AtPR-1 的表达。尽管如此，与 Col-0 植物相比，在拟南芥突变体 coi1 和 sid2-2（分别在茉莉酸感知和水杨酸合成方面有缺陷）中观察到类似的 AU4i 保护作用。因此，提出了 AU4i 保护作用和植物防御信号通路的独立性。AU4i 接种能够诱导花青素和酚类化合物的积累，以及苯丙氨酸解氨酶活性。此外，还评估了 AU4i 接种对植物细胞壁代谢的影响。结果，在含有来自接种拟南芥叶的细胞壁多糖的培养基中，灰质芽孢杆菌和核盘菌菌丝体生长减少。此外，AU4i 定植的叶子显示出参与半纤维素和果胶降解的基因（分别为 AtExp8 和 AtAra1）的下调和 AtPME3 的上调，AtPME3 是一种编码与果胶主链去酯化有关的假定果胶甲酯酶的基因。总之，我们的结果表明伯克霍尔德菌属。