Transcriptome and Expression Profiling Analysis of Recalcitrant Tea (Camellia sinensis L.) Seeds Sensitive to Dehydration

Abstract

The tea plant (Camellia sinensis (L.) O. Kuntze) is an economically important woody perennial nonalcoholic health beverage crop. Tea seeds are categorized as recalcitrant and are sensitive to dehydration treatment. However, the molecular basis of this phenomenon has not been investigated. Thus, we analyzed the genome-wide expression profiles of three dehydration stages using RNA-Seq and digital gene expression (DGE) technologies. We performed de novo assembly and obtained a total of 91,925 nonredundant unigenes, of which 58,472 were extensively annotated. By a hierarchical clustering of differentially expressed genes (DEGs), we found that 8929 DEGs were downregulated and 5875 DEGs were upregulated during dehydration treatment. A series of genes related to ABA biosynthesis and signal transduction, transcription factor, antioxidant enzyme, LEA protein, and proline metabolism that have been reported to function in dehydration process were found to be downregulated. Additionally, the expression profiles of 12 selected genes related to tea seed dehydration treatment were confirmed by qRT-PCR analysis. To our knowledge, this is the first genome-wide study elucidating the possible molecular mechanisms of sensitivity of recalcitrant tea seeds to dehydration. The results obtained in this study contribute to the preservation of tea seeds as genetic resources and can also be used to explore the mechanism of dehydration sensitivity of other recalcitrant seeds.

Genome-wide identification and expression analyses of the LEA protein gene family in tea plant reveal their involvement in seed development and abiotic stress responses

“…Additionally, some studies have revealed that LEA proteins are associated with seed desiccation tolerance 60,61 . In the current study, only two genes that encode LEA proteins were found to be significantly up-regulated, while relatively more CsLEA genes were found to be significantly down-regulated during the entire seed desiccation process, which is similar to our previous report 37 . This suggested that the CsLEA genes may not play an important protective role in tea seeds in response to desiccation treatment.…”

“…To investigate the involvement of the CsLEA genes in tea seed development, seeds were collected in the morning at seven different developmental time points (April 30, May 31, June 30, July 31, August 31, September 30, and October 31 in 2017). To investigate the relationship between the CsLEA genes and tea seed desiccation, seeds were collected at four different desiccation time stages (0, 3, 5, and 8 d), following the method described in our previous study 37 . Two-year-old cutting seedlings planted in pots were placed in an artificial climate chamber (Yiheng, Shanghai, China), and maintained at a constant temperature of 25 ± 1 °C with a constant photoperiod for at least one week before the application of abiotic stress treatments.…”

“…Meanwhile, tea seeds categorized as recalcitrant are highly sensitive to desiccation and cannot be used to preserve tea genetic resources for a long time 34 . Studies have shown the response of CsLEA genes to low temperature, drought, salinity, and desiccation stresses, which signifies their important roles in imparting stress tolerance 35–37 . Although 33 LEA genes have been identified based on the analysis of BLASTP searches against the tea plant genome 38 , our transcriptome analysis found additional CsLEA genes, which participated in the desiccation treatment process of recalcitrant tea seeds, had not been reported 37 .…”

“…Studies have shown the response of CsLEA genes to low temperature, drought, salinity, and desiccation stresses, which signifies their important roles in imparting stress tolerance 35–37 . Although 33 LEA genes have been identified based on the analysis of BLASTP searches against the tea plant genome 38 , our transcriptome analysis found additional CsLEA genes, which participated in the desiccation treatment process of recalcitrant tea seeds, had not been reported 37 . Furthermore, the biological functions of CsLEA genes that respond to high temperature and exogenous abscisic acid (ABA) stresses, particularly during seed development and desiccation in tea plant, remain unknown.…”

Unraveling the Roles of Regulatory Genes during Domestication of Cultivated Camellia: Evidence and Insights from Comparative and Evolutionary Genomics

“…A series of genes that have been reported to function in the dehydration process were found to be downregulated including ABA biosynthesis and signal transduction, transcription factor, antioxidant enzyme, etc. [ 21 ].…”