Fansuo Zeng

Rapid climate change is altering tree evolution, but how geography and climate shape genetic variation in temperate species remains unclear. This study integrated phenotypic, molecular marker, and climatic data for Fraxinus mandshurica in northeastern China to elucidate the drivers of population genetic differentiation and facilitate climate-resilient breeding. Phenotypic assessment of 209 half-sib families in a common garden experiment detected substantial variation across 17 seedling traits. Growth increment traits exhibited the highest phenotypic coefficients of variation, with basal diameter increment reaching 49.77%. Broad-sense heritability estimates ranged from 0.20 to 0.68, peaking in one-year seedling height. Seven SSR primer pairs amplified 56 polymorphic loci, with 67% of genetic variation partitioned within populations. Partial redundancy analysis demonstrated that climate independently explained 61.79% of genetic variation, versus 14.94% by geography, indicating isolation by environment rather than by distance. Using multi-trait FAI-BLUP analysis, 42 superior families were identified, representing the top 20% of all tested progenies. Two independent core germplasm collections were established, designated as the phenotypic core C1 derived from BLUP data and the molecular core C2 based on SSR markers, with only 10.0% overlap. The C1 core enriched genotypes with enhanced growth performance and drought resistance, while the C2 core maximized the retention of population-level genetic diversity. These findings demonstrate that precipitation of the driest month is the primary climatic driver of genetic differentiation in Fraxinus mandshurica, and establish an integrative dual-strategy germplasm framework for climate-resilient breeding programs.

Fraxinus mandshurica exhibits high tolerance to ash dieback and superior wood mechanical properties, yet the genomic basis of these dual traits remains incompletely understood. Here, we present a chromosome-scale genome assembly of the elite clone 'M8' and integrate comparative genomics with temporal transcriptomics to investigate its adaptive architecture. We show that recent tandem and proximal duplications have contributed to the diversification and candidate positive selection of the NLR immune repertoire. Transcriptomic profiling reveals a stage-associated deployment pattern, in which expressed NLR genes are enriched during the Transition Stage, consistent with reinforced immune surveillance during rapid xylem expansion. As development progresses, the Latewood Stage shifts toward phenylpropanoid metabolism, lignification-related programs, and structural reinforcement. We identify and experimentally validate a latewood-recruited FmNAC104–FmPRX1 candidate regulatory module, in which FmNAC104 binds to and activates the FmPRX1 promoter and promotes endogenous FmPRX1 expression. Formal NAC/PRX gene family analysis further supports an enlarged NAC/PRX repertoire relative to P. trichocarpa and clarifies the orthogroup status of the FmNAC104–FmPRX1 module among related ash species. Collectively, our findings support a 'fortified defense' working model in which F. mandshurica temporally coordinates immune-receptor diversification with latewood-associated structural reinforcement. This study provides a genomic resource and candidate targets for breeding programs aimed at improving wood quality and disease resilience in Fraxinus.

Drought is a major abiotic stressor that severely threatens forest tree growth and survival worldwide. The SQUAMOSA promoter binding protein-like (SPL) family is a group of plant-specific transcription factors that play important roles in plant growth, development, and environmental adaptation. Our study showed that overexpression of Fraxinus mandshurica SPL2 (FmSPL2) promotes lignin biosynthesis and enhances drought tolerance. Phenotypic analysis indicated that the stomatal aperture of FmSPL2-OE1 and FmSPL2-OE2 was reduced by 12.05% and 19.23%, respectively, compared to the wild type (WT). Additionally, the xylem width of the sixth internode in these lines increased by 26.07% and 25.93% relative to WT. Correspondingly, lignin content was elevated by 19.87% and 18.48% compared with WT, respectively. Under drought stress, the lignin content in FmSPL2-OE plants remained elevated compared to WT. Furthermore, the overexpression lines exhibited increased SOD and POD activities, accompanied by reduced levels of MDA, H₂O₂, and superoxide anion. Transcriptome analysis indicated significant upregulation of multiple genes involved in phenylpropanoid biosynthesis in FmSPL2-OE plants, including phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and 4-coumarate-CoA ligase (4CL). Moreover, the yeast one-hybrid and dual-luciferase reporter assays demonstrated that FmSPL2 directly binds to the promoter regions of phenylpropanoid-related genes like PAL, CAD, and PRX, thereby activating the expression of these genes and enhancing lignin biosynthesis. These results elucidate a novel function of FmSPL2 in enhancing drought tolerance through the regulation of phenylpropanoid pathway-mediated lignin accumulation.

UV-B radiation and drought majorly restrict plant growth, particularly in summer. ELONGATED HYPOCOTYL 5 (HY5), a bZIP transcription factor (TF), has a beneficial impact on photomorphogenesis. However, the sequence of HY5 from Betula platyphylla (BpHY5) has not been identified and the gene functions remain unclarified. We cloned the sequence of BpHY5, which was targeted to the nucleus. The hypocotyl phenotypes of heterologous expression in Arabidopsis thaliana and reverse mutation showed that BpHY5 is homologous to AtHY5. The expression of BpHY5 was increased in response to UV-B radiation, drought conditions, and the presence of abscisic acid (ABA). The overexpression of BpHY5 resulted in increased tolerance to UV-B radiation and drought and decreased ABA sensitivity with higher germination and greening rate, more developmental root system, stronger reactive oxygen species scavenging ability, and lower damage degree. The lignin content under UV-B condition of BpHY5/Col was higher than that of Col. Furthermore, overexpressing BpHY5 up-regulated the expression of genes related to tolerance (NCED3/9, ABI5, DREB2A, RD20, ERF4, NDB2, and APX2). In brief, the study suggests that BpHY5 from birch serves as a beneficial modulator of plant responses to UV-B radiation and drought stress.