Forest Botany and Tree Physiology, Goettingen Center for Molecular Biosciences (GZMB), University of Goettingen, Büsgenweg 2, Göttingen, 37077, Germany.
Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences and Goettingen Center for Molecular Biosciences (GZMB), University of Goettingen, Justus-von-Liebig-Weg 11, Göttingen, 37077, Germany.
Plant J. 2022 Jul;111(1):282-303. doi: 10.1111/tpj.15802. Epub 2022 May 27.
Xylem sap is the major transport route for nutrients from roots to shoots. In the present study, we investigated how variations in nitrogen (N) nutrition affected the metabolome and proteome of xylem sap and the growth of the xylem endophyte Brennaria salicis, and we also report transcriptional re-wiring of leaf defenses in poplar (Populus × canescens). We supplied poplars with high, intermediate or low concentrations of ammonium or nitrate. We identified 288 unique proteins in xylem sap. Approximately 85% of the xylem sap proteins were shared among ammonium- and nitrate-supplied plants. The number of proteins increased with increasing N supply but the major functional categories (catabolic processes, cell wall-related enzymes, defense) were unaffected. Ammonium nutrition caused higher abundances of amino acids and carbohydrates, whereas nitrate caused higher malate levels in xylem sap. Pipecolic acid and N-hydroxy-pipecolic acid increased, whereas salicylic acid and jasmonoyl-isoleucine decreased, with increasing N nutrition. Untargeted metabolome analyses revealed 2179 features in xylem sap, of which 863 were differentially affected by N treatments. We identified 124 metabolites, mainly from specialized metabolism of the groups of salicinoids, phenylpropanoids, phenolics, flavonoids, and benzoates. Their abundances increased with decreasing N, except coumarins. Brennaria salicis growth was reduced in nutrient-supplemented xylem sap of low- and high- NO -fed plants compared to that of NH -fed plants. The drastic changes in xylem sap composition caused massive changes in the transcriptional landscape of leaves and recruited defenses related to systemic acquired and induced systemic resistance. Our study uncovers unexpected complexity and variability of xylem composition with consequences for plant defenses.
木质部汁液是养分从根部向茎叶运输的主要途径。本研究调查了氮（N）营养变化如何影响木质部汁液的代谢组和蛋白质组以及木质部内生菌Brennaria salicis 的生长，并报告了杨树（Populus × canescens）叶片防御的转录重连。我们用高、中、低浓度的铵或硝酸盐供应杨树。我们在木质部汁液中鉴定出 288 种独特的蛋白质。大约 85%的木质部汁液蛋白质在铵和硝酸盐供应的植物中是共有的。随着 N 供应的增加，蛋白质的数量增加，但主要的功能类别（分解代谢过程、细胞壁相关酶、防御）不受影响。铵营养导致氨基酸和碳水化合物的丰度增加，而硝酸盐导致木质部汁液中苹果酸水平升高。随着 N 营养的增加，哌啶酸和 N-羟基-哌啶酸增加，而水杨酸和茉莉酸异亮氨酸减少。非靶向代谢组学分析显示木质部汁液中有 2179 种特征，其中 863 种受 N 处理的差异影响。我们鉴定出 124 种代谢物，主要来自水杨素类、苯丙素类、酚类、类黄酮类和苯甲酸酯类的特殊代谢物。除香豆素外，它们的丰度随着 N 的减少而增加。与 NH 喂养的植物相比，在低和高 NO 喂养的植物的补充营养的木质部汁液中，Brennaria salicis 的生长减少。木质部汁液组成的剧烈变化导致叶片转录景观发生巨大变化，并招募与系统获得和诱导的系统抗性相关的防御。我们的研究揭示了木质部组成的意想不到的复杂性和可变性，对植物防御产生影响。
