BackgroundMicroRNAs (miRNAs) are approximately 19 ~ 21 nucleotide noncoding RNAs produced by Dicer-catalyzed excision from stem-loop precursors. Many plant miRNAs have critical functions in development, nutrient homeostasis, abiotic stress responses, and pathogen responses via interaction with specific target mRNAs. Camellia sinensis is one of the most important commercial beverage crops in the world. However, miRNAs associated with cold stress tolerance in C. sinensis remains unexplored. The use of high-throughput sequencing can provide a much deeper understanding of miRNAs. To obtain more insight into the function of miRNAs in cold stress tolerance, Illumina sequencing of C. sinensis sRNA was conducted.ResultSolexa sequencing technology was used for high-throughput sequencing of the small RNA library from the cold treatment of tea leaves. To align the sequencing data with known plant miRNAs, we characterized 106 conserved C. sinensis miRNAs. In addition, 215 potential candidate miRNAs were found, among, which 98 candidates with star sequences were chosen as novel miRNAs. Both congruously and differentially regulated miRNAs were obtained, and cultivar-specific miRNAs were identified by microarray-based hybridization in response to cold stress. The results were also confirmed by quantitative real-time polymerase chain reaction. To confirm the targets of miRNAs, two degradome libraries from two treatments were constructed. According to degradome sequencing, 455 and 591 genes were identified as cleavage targets of miRNAs from cold treatments and control libraries, respectively, and 283 targets were present in both libraries. Functional analysis of these miRNA targets indicated their involvement in important activities, such as development, regulation of transcription, and stress response.ConclusionsWe discovered 31 up-regulated miRNAs and 43 down-regulated miRNAs in ‘Yingshuang’, and 46 up-regulated miRNA and 45 down-regulated miRNAs in ‘Baiye 1’ in response to cold stress, respectively. A total of 763 related target genes were detected by degradome sequencing. The RLM-5′RACE procedure was successfully used to map the cleavage sites in six target genes of C. sinensis. These findings reveal important information about the regulatory mechanism of miRNAs in C. sinensis, and promote the understanding of miRNA functions during the cold response. The miRNA genotype-specific expression model might explain the distinct cold sensitivities between tea lines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0271-x) contains supplementary material, which is available to authorized users.

Purple-leaf tea plants, as anthocyanin-rich cultivars, are valuable materials for manufacturing teas with unique colors or flavors. In this study, a new purple-leaf cultivar “Zixin” (“ZX”) was examined, and its biochemical variation and mechanism of leaf color change were elucidated. The metabolomes of leaves of “ZX” at completely purple, intermediately purple, and completely green stages were analyzed using ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-QTOF-MS). Metabolites in the flavonoid biosynthetic pathway remained at high levels in purple leaves, whereas intermediates of porphyrin and chlorophyll metabolism and carotenoid biosynthesis exhibited high levels in green leaves. In addition, fatty acid metabolism was more active in purple leaves, and steroids maintained higher levels in green leaves. Saponin, alcohol, organic acid, and terpenoid-related metabolites also changed significantly during the leaf color change process. Furthermore, the substance changes between “ZX” and “Zijuan” (a thoroughly studied purple-leaf cultivar) were also compared. The leaf color change in “Zijuan” was mainly caused by a decrease in flavonoids/anthocyanins. However, a decrease in flavonoids/anthocyanins, an enhancement of porphyrin, chlorophyll metabolism, carotenoid biosynthesis, and steroids, and a decrease in fatty acids synergistically caused the leaf color change in “ZX”. These findings will facilitate comprehensive research on the regulatory mechanisms of leaf color change in purple-leaf tea cultivars.

γ-Aminobutyric acid (GABA) is an important bioactive component of tea (Camellia sinensis) providing various health benefits. We studied GABA accumulation via the GABA shunt and polyamine degradation pathways under anoxia in tea leaves. Anoxia caused a ∼20-fold increment in GABA concentration, relative to fresh tea leaves. This increment was due to the increase of glutamate decarboxylase and diamine oxidase activities. Genes involved in GABA formation, such as CsGAD1 and CsGAD2, were significantly up-regulated by anoxia. The concentrations of putrescine and spermine, two substrates for GABA production, were also increased by anoxia. Treating tea leaves with aminoguanidine completely inhibited diamine oxidase activity during anoxia, but the concentration of GABA decreased by only ∼25%. We infer that about one-fourth of GABA formed in tea leaves under anoxia comes from the polyamine degradation pathway, opening the possibility of producing GABA tea based through the regulation of metabolism.

Longan (Dimocarpus longan Lour.) is an important tropical fruit tree crop. Accurate varietal identification is essential for germplasm management and breeding. Using longan transcriptome sequences from public databases, we developed single nucleotide polymorphism (SNP) markers; validated 60 SNPs in 50 longan germplasm accessions, including cultivated varieties and wild germplasm; and designated 25 SNP markers that unambiguously identified all tested longan varieties with high statistical rigor (P<0.0001). Multiple trees from the same clone were verified and off-type trees were identified. Diversity analysis revealed genetic relationships among analyzed accessions. Cultivated varieties differed significantly from wild populations (Fst=0.300; P<0.001), demonstrating untapped genetic diversity for germplasm conservation and utilization. Within cultivated varieties, apparent differences between varieties from China and those from Thailand and Hawaii indicated geographic patterns of genetic differentiation. These SNP markers provide a powerful tool to manage longan genetic resources and breeding, with accurate and efficient genotype identification.