BACKGROUND Fusarium circinatum, the causal agent of pitch canker disease, poses a serious threat to several Pinus species affecting plantations and nurseries. Although Pinus pinaster has shown moderate resistance to F. circinatum, the molecular mechanisms of defense in this host are still unknown. Phytohormones produced by the plant and by the pathogen are known to play a crucial role in determining the outcome of plant-pathogen interactions. Therefore, the aim of this study was to determine the role of phytohormones in F. circinatum virulence, that compromise host resistance. RESULTS A high quality P. pinaster de novo transcriptome assembly was generated, represented by 24,375 sequences from which 17,593 were full length genes, and utilized to determine the expression profiles of both organisms during the infection process at 3, 5 and 10 days post-inoculation using a dual RNA-sequencing approach. The moderate resistance shown by Pinus pinaster at the early time points may be explained by the expression profiles pertaining to early recognition of the pathogen, the induction of pathogenesis-related proteins and the activation of complex phytohormone signaling pathways that involves crosstalk between salicylic acid, jasmonic acid, ethylene and possibly auxins. Moreover, the expression of F. circinatum genes related to hormone biosynthesis suggests manipulation of the host phytohormone balance to its own benefit. CONCLUSIONS We hypothesize three key steps of host manipulation: perturbing ethylene homeostasis by fungal expression of genes related to ethylene biosynthesis, blocking jasmonic acid signaling by coronatine insensitive 1 (COI1) suppression, and preventing salicylic acid biosynthesis from the chorismate pathway by the synthesis of isochorismatase family hydrolase (ICSH) genes. These results warrant further testing in F. circinatum mutants to confirm the mechanism behind perturbing host phytohormone homeostasis.

中文翻译：

---

圆镰刀菌（Fusarium circinatum）攻击下的松树转录组。

背景技术圆角镰刀菌（Fusarium circinatum）是沥青溃疡病的病因，它对影响种植园和苗圃的几种松属树种构成了严重威胁。尽管Pinus pinaster对圆环镰孢表现出中等抗性，但该寄主中防御的分子机制仍然未知。已知由植物和病原体产生的植物激素在决定植物与病原体相互作用的结果中起关键作用。因此，本研究的目的是确定植物激素在危害宿主抗性的圆环镰刀菌毒力中的作用。结果产生了高质量的新P. pinaster de novo转录组，由24,375个序列代表，其中17,593个是全长基因，并被用于确定两种生物在感染过程中的表达谱（3，接种后5天和10天使用双重RNA测序方法。Pinus pinaster在早期时间点表现出的中度抗性可能是由与病原体的早期识别，致病相关蛋白的诱导以及涉及水杨酸，茉莉酸之间的串扰的复杂植物激素信号通路的激活有关的表达谱来解释的酸，乙烯和植物生长素。此外，与激素生物合成有关的圆环镰刀菌基因的表达表明，操纵宿主植物激素的平衡对其自身有利。结论我们假设了宿主操纵的三个关键步骤：通过真菌表达与乙烯生物合成相关的基因来扰动乙烯稳态，通过冠状动脉不敏感1（COI1）抑制阻断茉莉酸信号传递，并通过等轴线酶家族水解酶（ICSH）基因的合成来防止分支酸途径中水杨酸的生物合成。这些结果保证在圆环镰刀菌突变体中进行进一步测试，以证实干扰宿主植物激素稳态的机制。