Genome-wide identification of RNA editing sites in chloroplast transcripts and multiple organellar RNA editing factors in tea plant (Camellia sinensis L.): Insights into the albinism mechanism of tea leaves.

RNA editing is a post-transcriptional modification process, the chloroplast genes of which are involved in the process of chloroplast development in plant. However, the RNA editing sites of chloroplast genes remains unknown. In this study, we identified 39 RNA editing sites in 18 chloroplast genes from chloroplast genome of C. sinensis. Furthermore, the feature, structures and specificity of RNA editing sites were systematic analyzed. The differential editing efficiency were examined at 11 RNA editing sites among C. sinensis var. sinensis 'Huabai 1', 'Baiye 1' and 'Longjing 43'. Meanwhile, we identified 10 C. sinensis MORFs from five subgroups and performed comparative analyses of chromosome locations, duplication model and expression profiles. Expression analysis showed that the expression level of CsMORF9.2 was down-regulated significantly in 'Huabai 1' albino tea cultivar. This study provides a foundation for further reveal in the role of chloroplast RNA editing in albinism process of tea leaves.

Glutamine Synthetases Play a Vital Role in High Accumulation of Theanine in Tender Shoots of Albino Tea Germplasm "Huabai 1".

Theanine (N-ethyl-γ-l-glutamine) is a special nonprotein amino acid that contributes to the umami taste and health function of tea. Although recent studies on tea breeding have focused on albino tea because of its umami taste, a factor of higher theanine concentration, the mechanism of biosynthesis of l-theanine is still unclear. In this study, four glutamine synthetase genes (CsGSs) were obtained and functionally characterized by overexpressing them in Arabidopsis. The enzyme activities of the purified CsGS proteins from Escherichia coli were detected. The results showed that CsGSs have a dual function in the synthesis of glutamine and theanine in vivo and in vitro. Interestingly, l-theanine was abundantly synthesized in the tender shoots of "Huabai 1". In the white tender shoots, the cytosol CsGS1.2 might exhibit increased expression to compensate for decreasing levels of chloroplast CsGS2, which plays a vital role in high accumulation of theanine in "Huabai 1". In addition, CsGS2 was most likely the key l-theanine synthases in green tissues of tea. The present findings will provide basis for and considerably broaden the scope of understanding the function of CsGSs and the mechanism of l-theanine accumulation in the tender shoots of "Huabai 1", and will be useful for breeding and screening tea with high l-theanine content.