The Intron Retention Variant CsClpP3m Is Involved in Leaf Chlorosis in Some Tea Cultivars

Tea products made from chlorotic or albino leaves are very popular for their unique flavor. Probing into the molecular mechanisms underlying the chlorotic leaf phenotype is required to better understand the formation of these tea cultivars and aid in future practical breeding. In this study, transcriptional alterations of multiple subunit genes of the caseinolytic protease complex (Clp) in the chlorotic tea cultivar 'Yu-Jin-Xiang' (YJX) were found. Cultivar YJX possessed the intron retention variant of ClpP3, named as CsClpP3m, in addition to the non-mutated ClpP3. The mutated variant results in a truncated protein containing only 166 amino acid residues and lacks the catalytic triad S182-H206-D255. Quantitative analysis of two CsClpP3 variants in different leaves with varying degrees of chlorosis in YJX and analyses of different chlorotic tea cultivars revealed that the transcript ratios of CsClpP3m over CsClpP3 were negatively correlated with leaf chlorophyll contents. The chlorotic young leaf phenotype was also generated in the transgenic tobacco by suppressing ClpP3 using the RNAi method; complementation with non-mutated CsClpP3 rescued the wild-type phenotype, whereas CsClpP3m failed to complement. Taken together, CsClpP3m is involved in leaf chlorosis in YJX and some other tea cultivars in a dose-dependent manner, likely resulting from the failure of Clp complex assembly due to the truncated sequence of CsClpP3m. Our data shed light on the mechanisms controlling leaf chlorosis in tea plants.

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.

Improving Albino Tea Quality by Foliar Application of Glycinebetaine as a Green Regulator under Lower Temperature Conditions

White leaf No.1 (WL-1) is a low temperature-induced albino tea cultivar, which sticks out from tea plants with rich amino acids. Because harmonization of chloroplast ultrastructure integrity and lower chlorophyll contents during the albinism processes is much crucial for WL-1 production under extreme weather conditions, we carried out a field experiment to investigate the regulating effects of exogenous glycinebetaine (GB) on the chloroplast ultrastructure and quality constituents in young leaves of WL-1 at different albinism stages. The internal structure of chloroplasts degenerated at the albinistic stage, and chlorophyll contents were significantly lower than those at pre-albinistic and regreening stages. Spraying GB regulated etioplast-chloroplast transition, significantly increased epigallocatechin gallate, theanine, and caffeine contents, and lowered chlorophyll content in albinistic young leaves of WL-1, thus improving its quality in some aspects, maintaining special leaf color, exerting flavor and umami, and improving antioxidant and refreshing effects. Foliar application of GB is an efficient technical measure in practice.

Study on discrimination of white tea and albino tea based on near-infrared spectroscopy and chemometrics

BACKGROUND

White tea and albino tea have their own nutritional characteristics, but from the appearance they are quite similar to each other. It is not easy to distinguish them with existing analytical tools or by visual inspection. The current study proposed a rapid method to discriminate them based on near-infrared (NIR) spectroscopy associated with supervised pattern recognition methods.

RESULTS

For this purpose, discriminant partial least-squares (DPLS) and discriminant analysis (DA) were employed to build classification models on the basis of a reduced subset of wavenumbers and different pretreatment methods. A completely independent validation set was also used to test the model performance. The results of the DA model showed that with the SNV Karl Norris derivative spectral pre-treatment samples from the two different origins could be 100% correctly discriminated. Similarly, for the DPLS model, the best classification results were obtained with the multiplicative scattering correction (MSC) + first derivative spectral pre-treatments; the accuracy of identification was 98.48% for the calibration set and 100% for the validation set.

CONCLUSION

The overall results demonstrated that NIR spectroscopy with pattern recognition could be successfully applied to discriminate white tea and albino tea quickly and non-destructively without the need for various analytical determinations.