BACKGROUND Erwinia chrysanthemi (Ec) is a destructive pathogen which causes soft-rot diseases in diverse plant species including orchids. We investigated whether colonization of Oncidium roots by the endophytic fungus Piriformospora indica (Pi) restricts Ec-induced disease development in leaves, and whether this might be related to the regulation of nucleotide binding site-leucine rich repeat (NBS-LRR) Resistance (R) genes. RESULTS Root colonization of Oncidium stackings by Pi restricts progression of Ec-induced disease development in the leaves. Since Pi does not inhibit Ec growth on agar plates, we tested whether NBS-LRR R gene transcripts and the levels of their potential target miRNAs in Oncidium leaves might be regulated by Pi. Using bioinformatic tools, we first identified NBS-LRR R gene sequences from Oncidium, which are predicted to be targets of miRNAs. Among them, the expression of two R genes was repressed and the accumulation of several regulatory miRNA stimulated by Ec in the leaves of Oncidium plants. This correlated with the progression of disease development, jasmonic and salicylic acid accumulation, ethylene synthesis and H2O2 production after Ec infection of Oncidium leaves. Interestingly, root colonization by Pi restricted disease development in the leaves, and this was accompanied by higher expression levels of several defense-related R genes and lower expression level of their target miRNA. CONCLUSION Based on these data we propose that Pi controls the levels of NBS-LRR R mRNAs and their target miRNAs in leaves. This regulatory circuit correlates with the protection of Oncidium plants against Ec infection, and molecular and biochemical investigations will demonstrate in the future whether, and if so, to what extent these two observations are related to each other.

中文翻译：

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内生真菌印度梨孢子菌（Piriformospora indica）对兰花兰科植物根的定殖限制了菊花欧文氏菌的感染，刺激了NBS-LRR抗性基因转录本的积累并抑制了它们在叶片中的靶向微RNA。

背景技术金菊欧文氏杆菌（Erwinia chrysanthemi，Ec）是一种破坏性病原体，其在包括兰花在内的多种植物物种中引起软腐病。我们调查了内生真菌Piriformospora indica（Pi）对文心兰根的定殖是否限制了Ec诱导的叶片疾病的发展，以及这是否可能与核苷酸结合位点-富含亮氨酸的重复序列（NBS-LRR）的抗性调控有关（R ）基因。结果Pi引起的文心兰根的根定殖限制了Ec诱导的叶片中疾病发展的进程。由于Pi不会抑制琼脂平板上Ec的生长，因此我们测试了Oncidium叶片中NBS-LRR R基因的转录本及其潜在靶miRNA的水平是否可能受到Pi的调控。我们首先使用生物信息学工具从Oncidium中鉴定了NBS-LRR R基因序列，预计它们将成为miRNA的靶标。其中，抑制了两个R基因的表达，并在文心兰植物的叶片中抑制了Ec刺激的几种调节性miRNA的积累。这与Oncdium叶片Ec感染后疾病的发展，茉莉酸和水杨酸的积累，乙烯的合成以及H2O2的产生有关。有趣的是，Pi的根​​定植限制了叶片中的疾病发展，并伴有一些防御相关R基因的高表达水平和其靶miRNA的低表达水平。结论基于这些数据，我们建议Pi控制叶片中NBS-LRR R mRNA及其靶miRNA的水平。该调节回路与Oncidium植物对Ec感染的保护有关，