Univ Angers, Institut Agro, INRAE, IRHS, SFR QUASAV, F-49000, Angers, France.
Univ Angers, SFR QUASAV, F-49000, Angers, France.
BMC Genomics. 2021 Nov 22;22(1):843. doi: 10.1186/s12864-021-08157-1.
Scab is the most important fungal disease of apple and pear. Apple (Malus x domestica Borkh.) and European pear (Pyrus communis L.) are genetically related but they are hosts of two different fungal species: Venturia inaequalis for apple and V. pyrina for European pear. The apple/V. inaequalis pathosystem is quite well known, whereas knowledge about the pear/V. pyrina pathosystem is still limited. The aim of our study was to analyse the mode of action of a major resistance gene of apple (Rvi6) in transgenic apple and pear plants interacting with the two scab species (V. inaequalis and V. pyrina), in order to determine the degree of functional transferability between the two pathosystems.
Transgenic pear clones constitutively expressing the Rvi6 gene from apple were compared to a scab transgenic apple clone carrying the same construct. After inoculation in greenhouse with V. pyrina, strong defense reactions and very limited sporulation were observed on all transgenic pear clones tested. Microscopic observations revealed frequent aborted conidiophores in the Rvi6 transgenic pear / V. pyrina interaction. The macro- and microscopic observations were very comparable to the Rvi6 apple / V. inaequalis interaction. However, this resistance in pear proved variable according to the strain of V. pyrina, and one of the strains tested overcame the resistance of most of the transgenic pear clones. Comparative transcriptomic analyses of apple and pear resistant interactions with V. inaequalis and V. pyrina, respectively, revealed different cascades of molecular mechanisms downstream of the pathogen recognition by Rvi6 in the two species. Signal transduction was triggered in both species with calcium (and G-proteins in pear) and interconnected hormonal signaling (jasmonic acid in pear, auxins in apple and brassinosteroids in both species), without involvement of salicylic acid. This led to the induction of defense responses such as a remodeling of primary and secondary cell wall, lipids biosynthesis (galactolipids in apple and cutin and cuticular waxes in pear), systemic acquired resistance signal generation (in apple) or perception in distal tissues (in pear), and the biosynthesis of phenylpropanoids (flavonoids in apple but also lignin in pear).
This study is the first example of a successful intergeneric transfer of a resistance gene among Rosaceae, with a resistance gene functioning towards another species of pathogen.
疮痂病是苹果和梨最重要的真菌病害。苹果（Malus x domestica Borkh.）和欧洲梨（Pyrus communis L.）是遗传相关的，但它们是两种不同真菌物种的宿主：苹果疮痂病菌（Venturia inaequalis）和欧洲梨痂病菌（V. pyrina）。苹果/ V. inaequalis 病理系统相当知名，而有关梨/ V. pyrina 病理系统的知识仍然有限。我们研究的目的是分析苹果（Rvi6）主要抗性基因在与两种疮痂病（V. inaequalis 和 V. pyrina）相互作用的转基因苹果和梨植物中的作用模式，以确定两个病理系统之间功能转移的程度。
与携带相同构建体的转基因苹果抗疮痂克隆相比，连续表达来自苹果的 Rvi6 基因的转基因梨克隆在温室接种 V. pyrina 后，在所有测试的转基因梨克隆上观察到强烈的防御反应和非常有限的孢子形成。显微镜观察显示，在 Rvi6 转基因梨/ V. pyrina 相互作用中，频繁出现畸形的分生孢子梗。宏观和微观观察与 Rvi6 苹果/ V. inaequalis 相互作用非常相似。然而，梨中的这种抗性因 V. pyrina 的菌株而异，测试的一种菌株克服了大多数转基因梨克隆的抗性。分别对苹果和梨的 Rvi6 与 V. inaequalis 和 V. pyrina 抗性相互作用进行比较转录组分析，揭示了 Rvi6 在两个物种中识别病原菌后不同的分子机制级联反应。信号转导在两个物种中均由钙（和梨中的 G 蛋白）和相互连接的激素信号（梨中的茉莉酸、苹果中的生长素和两者中的油菜素）触发，而不涉及水杨酸。这导致了防御反应的诱导，例如初生和次生细胞壁的重塑、脂质生物合成（苹果中的半乳糖脂和梨中的角质和角质蜡）、系统获得性抗性信号生成（在苹果中）或在远端组织中的感知（在梨中），以及苯丙烷类生物合成（苹果中的类黄酮，但也包括梨中的木质素）。
这项研究是蔷薇科中成功的抗性基因在属间转移的首例实例，一种抗性基因对另一种病原体物种起作用。
