Department of Forest Growth, Silviculture & Genetics, Austrian Research Centre for Forests BFW, Seckendorff-Gudent-Weg 8, 1131, Vienna, Austria.
Department of Botany, University of Innsbruck, Sternwartestraße 15, 6020, Innsbruck, Austria.
BMC Genomics. 2022 Jun 13;23(1):435. doi: 10.1186/s12864-022-08661-y.
Needle rust caused by the fungus Chrysomyxa rhododendri causes significant growth decline and increased mortality of young Norway spruce trees in subalpine forests. Extremely rare trees with enhanced resistance represent promising candidates for practice-oriented reproduction approaches. They also enable the investigation of tree molecular defence and resistance mechanisms against this fungal disease. Here, we combined RNA-Seq, RT-qPCR and secondary metabolite analyses during a period of 38 days following natural infection to investigate differences in constitutive and infection-induced defence between the resistant genotype PRA-R and three susceptible genotypes.
Gene expression and secondary metabolites significantly differed among genotypes from day 7 on and revealed already known, but also novel candidate genes involved in spruce molecular defence against this pathogen. Several key genes related to (here and previously identified) spruce defence pathways to needle rust were differentially expressed in PRA-R compared to susceptible genotypes, both constitutively (in non-symptomatic needles) and infection-induced (in symptomatic needles). These genes encoded both new and well-known antifungal proteins such as endochitinases and chitinases. Specific genetic characteristics concurred with varying phenolic, terpene, and hormone needle contents in the resistant genotype, among them higher accumulation of several flavonoids (mainly kaempferol and taxifolin), stilbenes, geranyl acetone, α-ionone, abscisic acid and salicylic acid.
Combined transcriptional and metabolic profiling of the Norway spruce defence response to infection by C. rhododendri in adult trees under subalpine conditions confirmed the results previously gained on artificially infected young clones in the greenhouse, both regarding timing and development of infection, and providing new insights into genes and metabolic pathways involved. The comparison of genotypes with different degrees of susceptibility proved that several of the identified key genes are differently regulated in PRA-R, and that the resistant genotype combines a strong constitutive defence with an induced response in infected symptomatic needles following fungal invasion. Genetic and metabolic differences between the resistant and susceptible genotypes indicated a more effective hypersensitive response (HR) in needles of PRA-R that prevents penetration and spread of the rust fungus and leads to a lower proportion of symptomatic needles as well as reduced symptom development on the few affected needles.
由真菌黄杨栅锈菌引起的锈病会导致亚高山森林中年轻挪威云杉的生长严重下降和死亡率增加。具有增强抗性的极为罕见的树木是有前途的实践导向繁殖方法的候选者。它们还能够调查树分子防御和对这种真菌病的抗性机制。在这里，我们在自然感染后 38 天内结合 RNA-Seq、RT-qPCR 和次生代谢物分析，研究了抗性基因型 PRA-R 与三种易感基因型之间组成型和感染诱导防御的差异。
从第 7 天开始，基因型之间的基因表达和次生代谢物差异显著，并揭示了已知但也有新的候选基因参与云杉对这种病原体的分子防御。与易感基因型相比，PRA-R 中与（此处和以前鉴定的）云杉锈病防御途径相关的几个关键基因在组成型（在无症状针叶中）和感染诱导（在有症状针叶中）均有差异表达。这些基因编码新的和已知的抗真菌蛋白，如内切几丁质酶和几丁质酶。特定的遗传特征与抗性基因型中针状酚类、萜类和激素含量的变化一致，其中几种类黄酮（主要是山奈酚和杨梅素）、芪类、香叶基丙酮、α-紫罗兰酮、脱落酸和水杨酸的含量较高。
在亚高山条件下对成年树木感染黄杨栅锈菌的挪威云杉防御反应进行的转录组和代谢组联合分析，证实了以前在温室中人工感染的年轻克隆中获得的结果，无论是在感染的时间和发展方面，都为参与的基因和代谢途径提供了新的见解。不同易感程度基因型的比较证明，在 PRA-R 中，几种鉴定出的关键基因的调控方式不同，并且抗性基因型在真菌入侵后，将强烈的组成型防御与感染的有症状针叶中的诱导反应相结合。抗性和易感基因型之间的遗传和代谢差异表明，PRA-R 针叶中的超敏反应（HR）更为有效，可防止锈菌的穿透和扩散，并导致有症状针叶的比例较低，以及受影响针叶上的症状发展程度降低。
