Yushen Ma

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.

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.

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.

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.

Drought stress is a critical environmental factor that significantly impacts plant growth and productivity. However, the transcriptome analysis of differentially expressed genes in response to drought stress in Camellia oleifera Abel. is still unclear. This study analyzed the transcriptome sequencing data of C. oleifera under drought treatments. A total of 20,674 differentially expressed genes (DEGs) were identified under drought stress, with the number of DEGs increasing with the duration of drought. Specifically, 11,793 and 18,046 DEGs were detected after 8 and 15 days of drought treatment, respectively, including numerous upregulated and downregulated genes. Gene Ontology (GO) enrichment analysis showed that the DEGs were primarily involved in various biological processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that carbon metabolism, glyoxylate and dicarboxylate metabolism, proteasome, glycine, serine, and threonine metabolism were the main affected pathways. Among the DEGs, 376 protein kinases, 42 proteases, 168 transcription factor (TF) genes, and 152 other potential functional genes were identified, which may play significant roles in the drought response of C. oleifera. The expression of relevant functional genes was further validated using quantitative real-time PCR (qRT-PCR). These findings contribute to the comprehension of drought tolerance mechanisms in C. oleifera and bolster the identification of drought-resistant genes for molecular breeding purposes.