Institute of Integrative Biology Zürich, Plant Pathology Group, Swiss Federal Institute of Technology, Zürich, Switzerland.
PLoS One. 2013 Nov 4;8(11):e78457. doi: 10.1371/journal.pone.0078457. eCollection 2013.
Ontogenic scab resistance in apple leaves and fruits is a horizontal resistance against the plant pathogen Venturia inaequalis and is expressed as a decrease in disease symptoms and incidence with the ageing of the leaves. Several studies at the biochemical level tried to unveil the nature of this resistance; however, no conclusive results were reported. We decided therefore to investigate the genetic origin of this phenomenon by performing a full quantitative transcriptome sequencing and comparison of young (susceptible) and old (ontogenic resistant) leaves, infected or not with the pathogen. Two time points at 72 and 96 hours post-inoculation were chosen for RNA sampling and sequencing. Comparison between the different conditions (young and old leaves, inoculated or not) should allow the identification of differentially expressed genes which may represent different induced plant defence reactions leading to ontogenic resistance or may be the cause of a constitutive (uninoculated with the pathogen) shift toward resistance in old leaves. Differentially expressed genes were then characterised for their function by homology to A. thaliana and other plant genes, particularly looking for genes involved in pathways already suspected of appertaining to ontogenic resistance in apple or other hosts, or to plant defence mechanisms in general. IN THIS WORK, FIVE CANDIDATE GENES PUTATIVELY INVOLVED IN THE ONTOGENIC RESISTANCE OF APPLE WERE IDENTIFIED: a gene encoding an "enhanced disease susceptibility 1 protein" was found to be down-regulated in both uninoculated and inoculated old leaves at 96 hpi, while the other four genes encoding proteins (metallothionein3-like protein, lipoxygenase, lipid transfer protein, and a peroxidase 3) were found to be constitutively up-regulated in inoculated and uninoculated old leaves. The modulation of the five candidate genes has been validated using the real-time quantitative PCR. Thus, ontogenic resistance may be the result of the corresponding up- and down-regulation of these genes.
苹果叶片和果实的先天抗痂病能力是一种针对植物病原体梨火疫病菌的水平抗性，表现为叶片老化时疾病症状和发病率下降。在生化水平上，有几项研究试图揭示这种抗性的本质；然而，没有报告得出明确的结果。因此，我们决定通过对感染或未感染病原体的幼叶（易感）和老叶（先天抗性）进行全定量转录组测序和比较，来研究这种现象的遗传起源。在接种后 72 和 96 小时选择两个时间点进行 RNA 采样和测序。比较不同条件（幼叶和老叶、接种或不接种）应能识别差异表达的基因，这些基因可能代表导致先天抗性的不同诱导植物防御反应，或者可能是老叶中固有（未接种病原体）抗性转变的原因。然后通过与拟南芥和其他植物基因的同源性对差异表达基因进行功能特征分析，特别是寻找已怀疑与苹果或其他宿主的先天抗性或植物防御机制有关的基因。在这项工作中，鉴定了五个可能参与苹果先天抗性的候选基因：一个编码“增强疾病易感性 1 蛋白”的基因在未接种和接种的老叶中均在 96 hpi 时下调，而其他四个基因编码的蛋白质（金属硫蛋白 3 样蛋白、脂氧合酶、脂质转移蛋白和过氧化物酶 3）在接种和未接种的老叶中均被发现呈组成性上调。使用实时定量 PCR 验证了这五个候选基因的调节。因此，先天抗性可能是这些基因相应上调和下调的结果。
