Abstract
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.
Highlights
IntroductionLeaf pigments such as chlorophyll, carotenoids, and flavonoids (anthocyanins) are leaf color determinants
Leaf pigments such as chlorophyll, carotenoids, and flavonoids are leaf color determinants
Chlorotic tea cultivars are widely used in the tea industry on a large scale (Figure 1A); it is of greater urgency to uncover the mechanisms of tea leaf chlorosis
Summary
Leaf pigments such as chlorophyll, carotenoids, and flavonoids (anthocyanins) are leaf color determinants. Chlorophyll and carotenoids present in chloroplasts function as photosynthetic substances, receiving light energy for carbon assimilation Changes in their abundances can lead to dramatic changes in leaf photosynthetic capacity and efficiency, plant metabolism, responses to environmental fluctuation, growth, and development. The phenotypic development of these chlorotic leaves and initiation of their regreening are largely dependent on environmental conditions such as light intensity and temperature (Du et al, 2009; Wang et al, 2015; Shin et al, 2018) These tea cultivars are very different from some other plant mutants such as variegated barley (Li et al, 2019) and golden leaf cucumber (Gao et al, 2016), CsClpP3m Variant Involves in Chlorosis in which leaves possess abnormal color but do not regreen. Cultivars with convertible leaf color are highly desired by the tea industry because mature green leaves can maintain plant growth and regular productivity in successive years, while young pale (virescent) tea leaves can be used to produce a high-quality green tea with an enhanced savory (“umami”) taste and reduced astringency (Feng et al, 2014)
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