Xyloglucan endotransglycosylase/hydrolase (XTH) genes play an important role in plant resistance to abiotic stress. However, systematic studies of the response of Boehmeria nivea (ramie) XTH genes (BnXTHs) to cadmium (Cd) stress are lacking. We sought to identify the BnXTH-family genes in ramie through bioinformatics analyses and to investigate their responses to Cd stress. We identified 19 members of the BnXTH gene family from the ramie genome, referred to as BnXTH1-19, among which BnXTH18 and BnXTH19 were located on no chromosomes and the remaining genes were unevenly distributed across 11 chromosomes. The 19 members were divided into four groups, Groups I/II/IIIA/IIIB, according to their phylogenetic relationships, and these groups were supported by analyses of intron–exon structure and conserved motif composition. A highly conserved catalytic site (HDEIDFEFLG) was observed in all BnXTH proteins. Additionally, three gene pairs (BnXTH6–BnXTH16, BnXTH8–BnXTH9, and BnXTH17–BnXTH18) were obtained with a fragment and tandem-repeat event analysis of the ramie genome. An analysis of cisregulatory elements revealed that BnXTH expression might be regulated by multiple hormones and abiotic and biotic stress responses. In particular, 17 cisregulatory elements related to abiotic and biotic stress responses and 11 cisregulatory elements related to hormone responses were identified. We also found that most BnXTH genes responded to Cd stress, and BnXTH1, BnXTH3, BnXTH6, and BnXTH15 were most likely to contribute to the Cd tolerance of ramie, as evidenced by the substantial increases in expression under Cd treatment. Heterologous expression of BnXTH1, BnXTH6, and BnXTH15 significantly enhanced the Cd tolerance of transgenic yeast cells. These results suggest that the BnXTH gene family is involved in Cd stress responses, laying a theoretical foundation for functional studies of BnXTH genes and the innovative breeding of Cd-tolerant ramie.

Grafting serves as a crucial propagation technique for superior Camellia oleifera varieties, where rootstock–scion compatibility significantly determines survival and growth performance. To systematically evaluate grafting compatibility in this economically important woody oil crop, we examined 15 rootstock–scion combinations using ‘Xianglin 210’ as the scion, assessing growth traits and conducting physiological assays (enzymatic activities of SOD and POD and levels of ROS and IAA) at multiple timepoints (0–32 days post-grafting). The results demonstrated that Comb. 4 (Xianglin 27 rootstock) exhibited superior compatibility, characterized by systemic antioxidant activation (peaking at 4–8 DPG), rapid auxin accumulation (4 DPG), and efficient sugar allocation. Transcriptome sequencing and WGCNA analysis identified 3781 differentially expressed genes, with notable enrichment in stress response pathways (Hsp70, DnaJ) and auxin biosynthesis (YUCCA), while also revealing key hub genes (FKBP19) associated with graft-healing efficiency. These findings establish that successful grafting in C. oleifera depends on coordinated rapid redox regulation, auxin-mediated cell proliferation, and metabolic reprogramming, with Comb. 4 emerging as the optimal rootstock choice. The identified molecular markers not only advance our understanding of grafting mechanisms in woody plants but also provide valuable targets for future breeding programs aimed at improving grafting success rates in this important oil crop.

Xyloglucan endotransglucosylase/hydrolase (XTH) plays a significant role in plant responses and adaptation to abiotic stresses. However, the XTH gene family in Camellia oleifera remains largely unknown. Herein, 31 CoXTH genes from the C. oleifera genome, which were clustered into four evolutionary groups, were identified. Notably, CoXTH1, CoXTH6, CoXTH14, CoXTH28, and CoXTH31 showed significant upregulation under drought stress, suggesting their importance in stress responses. Furthermore, heterologous expression of CoXTH1, CoXTH14, and CoXTH28 in yeast improved yeast survival under drought stress. Overexpressing CoXTH1 in Arabidopsis thaliana significantly enhanced drought tolerance, characterized by improved seedling growth, increased antioxidant enzyme activity, and reduced reactive oxygen species (ROS) levels. Notably, transgenic expression of CoXTH1 significantly elevated the contents of xyloglucan, leading to increased cellulose, and hemicellulose contents in the plants. The elevated hemicellulose and cellulose strengthen the cell wall structure, maintaining cellular integrity and stability, and improving plant drought tolerance. These findings lay a foundation for understanding the functional roles of CoXTH genes and highlight CoXTH1 as a potential candidate gene for improving drought tolerance in C. oleifera and other woody crops.

Seed germination is a critical phase in the plant lifecycle of Camellia oleifera (oil tea), directly influencing seedling establishment and crop reproduction. In this study, we examined transcriptomic and physiological changes across five defined germination stages (G0–G4), from radicle dormancy to cotyledon emergence. Using RNA sequencing (RNA-seq), we assembled 169,652 unigenes and identified differentially expressed genes (DEGs) at each stage compared to G0, increasing from 1708 in G1 to 10,250 in G4. Functional enrichment analysis revealed upregulation of genes associated with cell wall organization, glucan metabolism, and Photosystem II assembly. Key genes involved in cell wall remodeling, including cellulose synthase (CESA), phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), caffeoyl-CoA O-methyltransferase (COMT), and peroxidase (POD) showed progressive activation during germination. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed dynamic regulation of phenylpropanoid and flavonoid biosynthesis, photosynthesis, carbohydrate metabolism, and hormone signaling pathways. Transcription factors such as indole-3-acetic acid (IAA), ABA-responsive element binding factor (ABF), and basic helix–loop–helix (bHLH) were upregulated, suggesting hormone-mediated regulation of dormancy release and seedling development. Physiologically, cytokinin (CTK) and IAA levels peaked in G4, antioxidant enzyme activities were highest in G2, and starch content increased toward later stages. These findings provide new insights into the molecular mechanisms underlying seed germination in C. oleifera and identify candidate genes relevant to rootstock breeding and nursery propagation.

As a key economic tree in southern China, Camellia oleifera faces severe yield losses under drought. Grafting onto drought-tolerant rootstocks offers a potential mitigation strategy. To elucidate the impact of rootstocks on the drought resistance of the superior Camellia oleifera Abel. cultivar “Xianglin 210”, grafted seedlings with five scion–rootstock combinations, were subjected to gradient drought stress. Key physiological and biochemical indices related to photosynthesis, antioxidant enzymes, and osmotic adjustment were measured. Drought resistance was comprehensively evaluated using membership function analysis, and the expression of stress-responsive genes was quantified via quantitative real-time PCR (qRT-PCR). The results demonstrated that under drought stress, (1) stomatal conductance (Gs) decreased by 31.2–48.7%, while instantaneous water use efficiency (WUE) increased by 18.5–35.4%; (2) proline (Pro) and soluble sugars (SS) accumulated significantly, with increases of 2.3–4.1-fold and 1.8–3.2-fold, respectively; (3) activities of antioxidant enzymes were enhanced by 56–127%, mitigating oxidative damage; (4) membership function analysis ranked drought resistance as follows: Xianglin 27 (0.812) > Guangxi Superior Germplasm (0.698) > C. yuhsienensis (0.654) > Hunan Superior Germplasm (0.591) > Xianglin 1 (0.523); (5) qRT-PCR revealed significant upregulation of ABA signaling pathway genes (CoPYL6, CoPP2C75/51/24/26, CoSnRK2.8, and CoABI5) and transcription factors (CoLHY and CoWRKY70), indicating activation of drought-responsive regulatory networks. These findings provide a theoretical foundation for selecting drought-tolerant rootstocks and optimizing cultivation practices in Camellia oleifera, and provide practical criteria for selecting drought-tolerant rootstocks, facilitating sustainable Camellia oleifera cultivation in water-limited regions.

Camellia oleifera Abel. is a unique woody edible oil tree species in China mainly distributed in red soil areas. Nitrogen is one of the important growth-limiting factors for C. oleifera, and the nitrogen form has a vital impact on the growth and development of the plants. Ammonium and nitrate are the two nitrogen forms that are maximally absorbed and utilized by the plants. Here, we used one-year-old seedlings of the main varieties of C. oleifera (‘Xianglin No. 1’, ‘Xianglin No. 27’, and ‘Xianglin No. 210’) to set up six experimental groups treated with different nitrogen forms ([${\mathrm{N}\mathrm{O}}_3^{-}$:${\mathrm{N}\mathrm{H}}_4^{+}$] 0:0, 10:0, 7:3, 5:5, 3:7, and 0:10) and investigated the effects of nitrogen on the vegetative growth and photosynthetic characteristics of the seedlings. This study showed that mixed nitrogen sources could significantly increase the seedling height, ground diameter, biomass accumulation, and photosynthesis efficiency. Transcriptome sequencing analysis led to the identification of 3561 differentially expressed genes in the leaves. Preliminary screening identified several key enzyme genes from nitrogen nutrient metabolic pathways that were differentially expressed among seedlings grown with different nitrogen forms, and their expression pattern changes were further characterized. All the results demonstrate that the same proportion of ammonium nitrate ratio promoted the expression of genes encoding glutamine synthetase and glutamate synthase, thereby improving nitrogen assimilation and utilization efficiency. This study could provide a theoretical basis for scientific and rational fertilization and the improvement of nitrogen utilization efficiency in C. oleifera seedlings.