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Different poplar varieties vary in their tolerance to certain pathogens. However, knowledge about molecular regulation and critical responses of resistant poplars during pathogen infection remains scarce. To investigate adaptive responses to canker disease caused by the bacterium Lonsdalea populi, we screened three poplar varieties with contrasting tolerance, including Populus deltoides. 'Zhonglin 2025' (2025), Populus × Euramericana. '74/76' (107) and Populus tomentosa cv 'henan' (P. tomentosa). Transcriptomic analysis revealed significant changes in the expression levels of defence‐related genes in different poplar varieties in response to infection, which reshaped the PTI and ETI processes. Intriguingly, photosynthesis‐related genes were found to be highly expressed in the resistant variety, whereas the opposite was observed in the susceptible variety. Susceptible poplars maintained the activation of defence‐related genes during early period of onset, which restricted the expression of photosynthesis‐related and auxin signal‐related genes. Furthermore, combined with metabolomic analysis, differences in the content of antibacterial substances and key differentially expressed genes in phenylpropane and flavonoid biosynthesis pathways were identified. Delayed induction of catechin in the susceptible variety and it's in vitro antibacterial activity were considered to be one of the important reasons for the differences in resistance to L. populi compared with the resistant variety, which is of practical interest for tree breeding. Moreover, the trade‐off between growth and defence observed among the three poplar varieties during infection provides new insights into the multilevel regulatory circuits in tree‐pathogen interactions. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an important element in numerous metabolic reactions and signalling pathways, but the molecular details of these pathways remain largely unknown. In this study, physiological, transcriptome and metabolite analyses of apple leaves and roots were compared under different P conditions. The results showed that different P stresses influenced phenotypic characteristics, soil plant analytical development (SPAD) values and the contents of flavonoids and anthocyanins in apple seedlings. The contents of hydrogen peroxide (H 2 O 2) and malondialdehyde (MDA) and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), acid phosphatase (ACP) and purple acid phosphatase (PAP) were also affected by different P stresses. In addition, RNA sequencing (RNA-seq) was used to characterize the influence of different P stresses on apple seedlings. Compared with control apple plants, there were 1246 and 1183 differentially expressed genes (DEGs) in leaves and roots under the low-P treatment and 60 and 1030 DEGs in leaves and roots under the high-P treatment, respectively. Gene Ontology (GO) analysis indicated that apple trees might change their responses to metabolic processes, cell proliferation, regulation of biological processes, reactive oxygen species metabolic processes and flavonoid metabolic processes under P stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further indicated that DEGs act on the mitogen-activated protein kinase (MAPK) signalling pathway, flavonoid biosynthesis, phenylpropanoid biosynthesis, and ATP-binding cassette (ABC) transporters. The metabolome analysis revealed that the levels of most amino acids and their derivatives, organic acids and flavonoids in roots treated with low-P stress were higher than those in roots of apple seedlings under control growth conditions. Apple seedlings regulate the flavonoid pathway to respond to different phosphorus environments. The results provide a framework for understanding the metabolic processes underlying different P responses and provide a foundation for improving the utilization efficiency of P in apple trees. • Physiological, transcriptome and metabolite analyses of apple leaves and roots were compared under different phosphorus conditions. • RNA-Seq was used to characterize the influence of different P tolerances in apple seedlings. • The metabolome analysis revealed that most amino acids and derivatives, organic acids and flavonoids in LP roots were higher than those in CK roots in apple seedlings under different P conditions. • Apple seedlings regulate the flavonoid pathway to respond to different phosphorus environments. [ABSTRACT FROM AUTHOR]

• Physiological, transcriptome and metabolite analyses of apple leaves and roots were compared under different nitrogen conditions. • Different N stresses influenced plant growth and physiological characteristics. • RNA-Seq was used to characterize the influence of different N tolerance in apple seedlings. • The metabolome analysis revealed that most amino acids and derivatives, nucleotides and derivatives, and lipids decreased in LP leaves, but increased in roots compared with CK in apple seedlings. • Apple seedlings through regulated the carbon and nitrogen metabolism, and flavonoid pathway to respond to the different nitrogen environments. Nitrogen (N) is an essential element for plant growth and development. In this study, physiological, transcriptome and metabolite analyses of apple leaves and roots were compared under different N conditions. The results indicated that different N stresses influenced plant growth, the content of soil plant analytical development (SPAD) value and photosynthesis in apple seedlings. The content of hydrogen peroxide (H 2 O 2), and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamine antinotransferase (GOGAT) were also affected by different N stresses. RNA-Seq was used to analysis the influence of different N tolerances in apple seedlings. Gene Ontology (GO) analysis of differentially expressed genes (DEGs) indicated that apple trees might affect the responses to photosynthesis, organic hydroxy compound biosynthetic process, and secondary metabolite biosynthetic process under N stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs focused on photosynthesis and secondary metabolite biosynthetic process. There were 527 differential metabolites in LNL/CKL, 157 in HNL/CKL, 477 in LNR/CKR, and 232 in HNR/CKR. The metabolome analysis indicated that total of 1004 and 389 significant differential metabolites were identified under low N and high N conditions in apple. Apple seedlings regulate the carbon metabolism, nitrogen metabolism and flavonoid pathway to adapt the different nitrogen environments. This research provide understanding for the metabolic processes underlying different N responses and provide a foundation for improving the efficiency of N use in apple trees. [ABSTRACT FROM AUTHOR]