Pu’an County, located in southwestern Guizhou Province, China, is one of the original habitats for wild tea plants. It is renowned not only as the “Home of Ancient Tea Trees in China” but also as the “Core Production Area for High-Quality Early Tea in China”. The wild ancient Camellia tetracocca tea trees are considered “living fossil”. Understanding the genetic diversity of wild ancient C. tetracocca in Pu’an, Guizhou, is of great significance for addressing conservation concerns and mitigating genetic erosion in this endemic species. This study investigates the genetic diversity and population structure of wild ancient C. tetracocca tea plants in Pu’an County to support the development of conservation strategies. We genotyped 138 ancient wild C. tetracocca specimens using 40 intron-length polymorphism markers. A total of 180 alleles were detected, with the allele numbers per locus ranging from 2 to 10 and an average of 4.50. The number of effective alleles varied from 1.36 to 8.01, with an average of 2.86. The Shannon information index ranged from 0.28 to 2.19, with an average of 1.10. Nei’s gene diversity index ranged from 0.14 to 0.88, with an average of 0.58. The polymorphic information content (PIC) varied from 0.14 to 0.85, with an average of 0.58. Our findings indicate that the genetic diversity of wild ancient C. tetracocca tea plants in Pu’an is high. Specifically, the genetic diversity in Qingshan Township surpassed that in Xindian Township. Analysis of molecular variance indicated that 91.59% of the genetic variation occurred within the subpopulations, suggesting limited differentiation. Despite their geographical separation, populations from Qingshan and Xindian showed a complex genetic relationship (F_ST = 0.04). STRUCTURE analysis identified three distinct genetic clusters, indicating a complex demographic history. These findings underscore the conservation significance of wild C. tetracocca populations in Pu’an and highlight the need for conservation strategies that prioritize the protection of genetically diverse subpopulations, especially in the Qingshan region.

Temperature stress is a major environmental factor that limits the growth of cucumber (Cucumis sativus L.). Melatonin has been implicated in plant responses to abiotic stress; however, its transcriptional effects on cucumber under high- and low-temperature conditions remain poorly understood. In this study, cucumber seedlings were exposed to 25 °C, 40 °C, or 4 °C, with or without exogenous melatonin treatment at 75 μmol·L⁻¹, and their transcriptional responses were investigated using RNA sequencing (RNA-seq). Both high- and low-temperature treatments caused varying degrees of seedling wilting, whereas this phenotype was partially alleviated by melatonin application. Transcriptome analysis identified 7488 and 3400 differentially expressed genes in response to high and low temperatures, respectively, indicating both shared and temperature-specific transcriptional responses. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that pathways related to plant hormone signal transduction, phenylpropanoid biosynthesis, and protein processing in the endoplasmic reticulum were significantly enriched in multiple comparisons. Further analysis revealed that melatonin treatment altered the expression patterns of several hormone signaling-related genes and transcription factors, including members of the ERF, MYB, WRKY, and bHLH families. Notably, hormone signaling components exhibited distinct transcriptional responses under high- and low-temperature conditions. The expression trends of selected genes determined by quantitative real-time polymerase chain reaction (qRT-PCR) were generally consistent with the RNA-seq results. Collectively, exogenous melatonin application was associated with reduced wilting symptoms and coordinated transcriptional changes in hormone signaling pathways under temperature stress. These findings provide a basis for further elucidating the molecular mechanisms underlying melatonin-mediated temperature adaptation in cucumber seedlings.