Excessive nitrogen (N) application may induce powdery mildew (PM) in perennial grasses, but the resistance mechanisms to PM remain unclear. This study evaluated the physiological and molecular mechanisms of PM resistance affected by N supplies in Kentucky bluegrass (Poa pratensis L.). Cultivar ‘Bluemoon’ (N tolerant) and ‘Balin’ (N sensitive) were treated with low N (0.5 mM), normal N (15 mM), and high N (30 mM) for 21 d in a greenhouse. With increasing N levels, the disease growth was more severe in ‘Balin’ than in ‘Bluemoon’. RNA-seq and weighted gene coexpression network analysis revealed that the PpGS1.1 gene encoding glutamine synthetase was a potential hub gene for PM resistance after comparisons across cultivars and N treatments. The N metabolism pathway was connected with the plant-pathogen interaction pathway via PpGS1.1. The expression of PpGS1.1 in rice protoplasts indicated that the protein was located in the nucleus and cytoplasm. Overexpression of PpGS1.1 in wild type Kentucky bluegrass increased carbon and N contents, and the transgenic plants became more susceptible to PM with a lower wax density. The most differentially expressed genes (DEGs) for N metabolism were upregulated and DEGs for fatty acid metabolism pathway were downregulated in the overexpression lines. The results elucidated mechanisms of PM resistance in relation to N metabolism in Kentucky bluegrass.

中文翻译：

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谷氨酰胺合成酶基因 PpGS1.1 负调控肯塔基早熟禾的白粉病抗性

过量施氮 (N) 可能会在多年生草本植物中诱发白粉病 (PM)，但对 PM 的抗性机制仍不清楚。本研究评估了肯塔基早熟禾 (Poa pratensis L.) 中受 N 供给影响的 PM 抗性的生理和分子机制。在温室中用低氮 (0.5 mM)、正常氮 (15 mM) 和高氮 (30 mM) 处理品种“Bluemoon”（N 耐受性）和“Balin”（N 敏感）21 天。随着 N 水平的增加，'Balin' 的病害生长比 'Bluemoon' 更严重。RNA-seq 和加权基因共表达网络分析表明，在比较不同品种和 N 处理后，编码谷氨酰胺合成酶的 PpGS1.1 基因是潜在的 PM 抗性中枢基因。N代谢途径通过PpGS1.1与植物-病原体相互作用途径相连。PpGS1.1在水稻原生质体中的表达表明该蛋白位于细胞核和细胞质中。PpGS1.1 在野生型肯塔基蓝草中的过表达增加了碳和氮含量，并且转基因植物变得更容易受到蜡密度较低的 PM 的影响。在过表达品系中，N 代谢最差异表达的基因 (DEG) 被上调，脂肪酸代谢途径的 DEG 被下调。结果阐明了与肯塔基早熟禾 N 代谢相关的 PM 抗性机制。在过表达品系中，N 代谢最差异表达的基因 (DEG) 被上调，脂肪酸代谢途径的 DEG 被下调。结果阐明了与肯塔基早熟禾 N 代谢相关的 PM 抗性机制。在过表达品系中，N 代谢最差异表达的基因 (DEG) 被上调，脂肪酸代谢途径的 DEG 被下调。结果阐明了与肯塔基早熟禾 N 代谢相关的 PM 抗性机制。