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Advances in carbohydrate metabolism prompted its essential role in defense priming and sweet immunity during plant-pathogen interactions. Nevertheless, upstream responding enzymes in the sucrose metabolic pathway and associated carbohydrate derivatives underlying fungal pathogen challenges remain to be deciphered in Populus, a model tree species. In silico deduction of genomic features, including phylogenies, exon/intron distributions, cis-regulatory elements, and chromosomal localization, identified 59 enzyme genes (11 families) in the Populus genome. Spatiotemporal expression of the transcriptome and the quantitative real-time PCR revealed a minuscule number of isogenes that were predominantly expressed in roots. Upon the pathogenic Fusarium solani (Fs) exposure, dynamic changes in the transcriptomics atlas and experimental evaluation verified Susy (PtSusy2 and 3), CWI (PtCWI3), VI (PtVI2), HK (PtHK6), FK (PtFK6), and UGPase (PtUGP2) families, displaying promotions in their expressions at 48 and 72 h of post-inoculation (hpi). Using the gas chromatography-mass spectrometry (GC-MS)-based non-targeted metabolomics combined with a high-performance ion chromatography system (HPICS), approximately 307 metabolites (13 categories) were annotated that led to the quantification of 46 carbohydrates, showing marked changes between three compared groups. By contrast, some sugars (e.g., sorbitol, L-arabitol, trehalose, and galacturonic acid) exhibited a higher accumulation at 72 hpi than 0 hpi, while levels of α-lactose and glucose decreased, facilitating them as potential signaling molecules. The systematic overview of multi-omics approaches to dissect the effects of Fs infection provides theoretical cues for understanding defense immunity depending on fine-tuned Suc metabolic gene clusters and synergistically linked carbohydrate pools in trees., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Integration of the pectin homogalacturonan (HG) integrity and remodeling into defense immunity facilitates building blocks of stress resilience within the host and pathogen interactions in the forests. Recent advances in apoplastic pectin methylesterases (PMEs) and coordinated PME inhibitors (PMEIs) deployed immune signaling, highlighting their critical roles in regulating biotic stress adaptation. Nevertheless, the PME and PMEI multiple isoenzyme families involved in defense priming in the model tree species are largely unknown. The in silico demonstration of the molecular profile identified 70 PME- (50 type-I proPME and 20 type-II PME) and 49 PMEI-encoding genes in the Populus genome. Evaluation of the transcript abundance verified 20 PtproPMEs and 18 PtPMEIs that showed predominant expression in the root and genetic redundancy for type-II PtPMEs. Dynamic changes in the transcriptome and experimental evaluation revealed a minuscule number of type-I proPMEs and PMEIs that showed marked promotions during a time-course Fusarium solani (Fs) infection. Using GC/LC-mass-based non-targeted metabolomics to inspect structure-related carbohydrates and PME activities suggested a correlation between proPME - PMEI co-expression and deformed pectin HG biosynthesis. Further functional examination of the enzyme inhibitory affinities of recombinant PtPMEI1 and 39 in vitro and apoplastic patterns suggested a clustering of the type-I proPME in the regulation of the innate immunity by maintaining homeostasis of the pectin HG de-methylesterification (DME) in the cell wall. The coherent omics-wide survey of the fungi pathogen-induced PME-PMEIs and disturbed carbohydrate accumulation provide theoretical cues for in-depth mining of the biological significance of the underlying immune signaling networks within an apoplastic niche in trees. • Molecular dissection of Populus PME/PMEI families. • ProPME-PMEI were co-induced upon F. solani infection. • PtPMEI1 and 39 hinted defense immunity. [ABSTRACT FROM AUTHOR]