Department of Horticulture, Zhejiang University, Hangzhou, China.
College of Horticulture and Plant Protection, Henan University of Science and Technology, Luoyang, China.
Plant Cell Environ. 2021 May;44(5):1596-1610. doi: 10.1111/pce.14019. Epub 2021 Feb 21.
Nitrogen (N) influences a myriad of physiological processes while its effects on plant defences and the underlying mechanisms are largely unknown. Here, the interaction between tomato and pathogens was examined under four N regimes (sole NO or mixed NO /NH of total 1 and 7 mM N, denoting low and high N regimes, respectively) followed by inoculation with two bacterial pathogens, Pseudomonas syringae and Ralstonia solanacearum. Tomato immunity against both pathogens was generally higher under low N as well as NO as the sole N source. The disease susceptibility was reduced by silencing N metabolism genes such as NR, NiR and Fd-GOGAT, while increased in NiR1-overexpressed plants. Further studies demonstrated that the N-modulated defence was dependent on the salicylic acid (SA) defence pathway. Low N as well as the silencing of N metabolism genes increased the SA levels and transcripts of its maker genes, and low N-enhanced defence was blocked in NahG transgenic tomato plants that do not accumulate SA, while exogenous SA application attenuated the susceptibility of OE-NiR1. The study provides insights into the mechanisms of how nitrogen fertilization and metabolism affect plant immunity in tomato, which might be useful for designing effective agronomic strategies for the management of N supply.
氮（N）影响着许多生理过程，但其对植物防御的影响及其潜在机制在很大程度上尚不清楚。在这里，我们在四种氮供应水平（单独的硝酸盐（NO）或混合的硝酸盐/氨（NO/ NH），总氮供应分别为 1 和 7mM，分别表示低氮和高氮水平）下，研究了番茄与病原体之间的相互作用，随后用两种细菌病原体（丁香假单胞菌和茄青枯假单胞菌）进行接种。在低氮和单独使用硝酸盐作为氮源的情况下，番茄对两种病原体的免疫力通常更高。沉默氮代谢基因，如硝酸还原酶（NR）、亚硝酸盐还原酶（NiR）和铁氧还蛋白-谷氨酸合酶（Fd-GOGAT），会降低植物的易感性，而 NiR1 过表达植株的易感性则会增加。进一步的研究表明，氮调控的防御依赖于水杨酸（SA）防御途径。低氮水平以及氮代谢基因的沉默会增加 SA 水平和其标记基因的转录，而在不积累 SA 的 NahG 转基因番茄植株中，低氮增强的防御作用被阻断，而外源 SA 的应用则削弱了 OE-NiR1 植株的易感性。该研究深入了解了氮施肥和代谢如何影响番茄植物免疫力的机制，这可能对设计有效的农业策略来管理氮供应有用。
