Integrated Analysis of Long Non-coding RNAs (lncRNAs) and mRNAs Reveals the Regulatory Role of lncRNAs Associated With Salt Resistance in Camellia sinensis.

Tea plant (Camellia sinensis), an important economic crop, is seriously affected by various abiotic stresses, including salt stress, which severely diminishes its widespread planting. However, little is known about the roles of long non-coding RNAs (lncRNAs) in transcriptional regulation under salt stress. In this study, high-throughput sequencing of tea shoots under salt-stress and control conditions was performed. Through sequencing analysis, 16,452 unique lncRNAs were identified, including 172 differentially expressed lncRNAs (DE-lncRNAs). The results of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of their cis- and trans-target genes showed that these DE-lncRNAs play important roles in many pathways such as the galactinol synthase (GOLS), calcium signaling pathway, and interact with transcription factors (TFs) under salt stress. The data from the gene-specific antisense oligodeoxynucleotide-mediated reduction in the lncRNA MSTRG.139242.1 and its predicted interacting gene, TEA027212.1 (Ca2+-ATPase 13), in tea leaves revealed that MSTRG.139242.1 may function in the response of tea plants to high salinity. In addition, 12 lncRNAs were predicted to be target mimics of 17 known mature miRNAs, such as miR156, that are related to the salt-stress response in C. sinensis. Our results provide new insights into lncRNAs as ubiquitous regulators in response to salt stress in tea plants.

Overexpression of CsSnRK2.5 increases tolerance to drought stress in transgenic Arabidopsis.

Drought is a major factor limiting crop productivity and quality. Sucrose non-fermenting-1 (SNF1)-related protein kinase 2s (SnRK2s) play critical roles in plant abiotic stress responses, especially in drought stress. However, knowledge regarding the functional roles of SnRK2s in drought stress and their underlying mechanisms is relatively limited in tea plant. In this study, CsSnRK2.5, a PEG 6000- and ABA-induced SnRK2 gene from tea plant, was overexpressed in Arabidopsis to investigate its potential function in drought stress response. The results showed that overexpression of CsSnRK2.5 resulted in enhanced drought tolerance, as indicated by an amelioration of the changes in various physiological indexes, including a decreased rate of water loss and decreased accumulation of ROS and MDA. In addition, CsSnRK2.5 overexpression conferred hypersensitivity to exogenous ABA, and transgenic plants exhibited improved ABA-mediated stomatal closure compared to WT plants. Moreover, the expression of some stress response genes, including AtRAB18 and AtRD29b, was more strongly induced in transgenic plants than in the WT when subjected to ABA and drought treatments. Taken together, our results indicate that CsSnRK2.5 is a positive regulator of ABA-regulated drought stress responses.

Genome-wide identification and characterization of the CsSnRK2 family in Camellia sinensis.

The sucrose nonfermenting 1 (SNF1)-related protein kinase 2 (SnRK2) genes play central roles in plant stress signal transduction. In this study, 8 SnRK2 genes were identified from the tea plant genome database and named CsSnRK2.1-8. Phylogenetic analysis showed that the CsSnRK2 genes were classifiable into three groups, similar to those of Arabidopsis thaliana, Oryza sativa and maize. The coding sequences (CDSs) of all CsSnRK2s were separated by eight introns, and their exon-intron organizations exhibited high similarity to those of other plants. The fluorescence of GFP fused with CsSnRK2.3 was detected in only the cytoplasm, while the rest of the proteins showed GFP signal in both the nucleus and the cytoplasm. The results of the expression patterns of the CsSnRK2 genes showed that CsSnRK2s were differentially induced by salt, polyethylene glycol (PEG) and abscisic acid (ABA) stress. Interestingly, The expression of CsSnRK2.3 was inhibited by ABA, suggesting the complicated roles of CsSnRK2s in the ABA signal transduction pathway. Some CsSnRK2 gene pairs showed significant expression change correlations under stresses, indicating that CsSnRK2s might exhibit synergistic effects of signal regulation in response to various stresses. In summary, this comprehensive analysis will facilitate further studies of the SnRK2 family of Camellia sinensis and provide useful information for the functional validation of CsSnRK2s.