Unlocking the green code: how CsCHLI drives chlorophyll synthesis in tea plants
image: (a) Leaf phenotypes of BY1, SC1, and LJ43 plants. (b) Transmission electron microscope images of leaf ultrastructures. (c) Chlorophyll content in the BY1, SC1, and LJ43 leaves. (d) Expression patterns of CsCHLI, CsCHLD, and CsCHLH genes in BY1, SC1, and LJ43 leaves. BY1, Baiye 1; SC1, Shaancha1; LJ43, Longjing43. * means p ≤ 0.05.
Credit: The authors
This discovery helps explain the molecular basis of albino tea phenotypes and offers new avenues for breeding high-quality tea cultivars with distinctive appearance and flavor. The research also demonstrates that overexpression of CsCHLI can restore normal green coloration in chlorophyll-deficient plants, highlighting its potential as a genetic target for photosynthetic enhancement.
Chlorophyll not only enables photosynthesis but also determines the vibrant green color of tea leaves, directly influencing their economic value and consumer appeal. Albino or etiolated tea cultivars, like 'Baiye 1', are prized for their high amino acid content and delicate flavor but suffer from low chlorophyll levels. This color deficiency is believed to be linked to alterations in genes involved in chlorophyll metabolism, particularly the magnesium chelatase enzyme complex, which initiates the first committed step of chlorophyll synthesis. Understanding how its subunits interact and function is vital for decoding the mechanisms behind tea leaf pigmentation. Based on these challenges, an investigation into the role of CsCHLI, a subunit of magnesium chelatase, was conducted.
A study (DOI: 10.48130/bpr-0023-0037) published in Beverage Plant Research on 1 February 2024 by Yuefang Gao’s team, Northwest A & F University, reveals how CsCHLI contributes to leaf coloration and offers insight into the albinism mechanisms of elite tea cultivars.
To elucidate the role of CsCHLI in tea leaf chlorophyll biosynthesis, researchers employed a series of molecular, structural, and functional analyses. They began by assessing leaf ultrastructure, chlorophyll content, and gene expression levels in both albino (BY1) and green tea cultivars. Transmission electron microscopy revealed that BY1 leaves exhibited fewer chloroplasts with disrupted thylakoid structures and lacked starch granules, consistent with their pale appearance. Chlorophyll a and b levels were significantly lower in BY1 compared to green cultivars SC1 and LJ43. RT-qPCR further confirmed a pronounced decline in CsCHLI expression in BY1, suggesting a key role in chlorophyll production. To characterize CsCHLI, the full-length gene was cloned and analyzed, revealing a 1275 bp sequence encoding a 424-amino acid protein with conserved ATPase domains, including Walker A/B and sensor motifs essential for Mg²⁺-chelatase activity. Phylogenetic analysis placed CsCHLI within the dicot clade, closely related to Actinidia chinensis, indicating evolutionary conservation. Subcellular localization experiments using CsCHLI-EYFP fusion constructs demonstrated chloroplast-specific targeting. Protein-protein interaction studies using yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays revealed that CsCHLI could form homodimers and also interact with CsCHLD and CsCHLH, forming part of the chelatase complex. Finally, functional validation was performed in Arabidopsis thaliana, where overexpression of CsCHLI in the chlorophyll-deficient atchli1 mutant partially rescued the yellow-leaf phenotype and restored chlorophyll levels, while maintaining correct chloroplast localization. Together, these results confirm that CsCHLI is a vital component of the Mg²⁺-chelatase complex, crucial for chlorophyll biosynthesis in tea, and its dysfunction may underlie albinism in certain cultivars.
This study offers a genetic explanation for the albino phenotypes of elite tea cultivars and identifies CsCHLI as a promising target for molecular breeding. Manipulating this gene could enable the development of tea varieties with optimized pigment profiles, enhanced photosynthetic capacity, and unique flavor properties. Beyond tea, the findings could be applied to improve chlorophyll metabolism in other crop species, especially under stress conditions affecting pigment synthesis.
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References
DOI
Original Source URL
https://doi.org/10.48130/bpr-0023-0037
Funding information
This work was financially supported by the National Natural Science Foundation of China (31700612), and the Key Research and Development Program of Shaanxi Province (2021ZDLNY04-03, 2023-YBNY-145).
About Beverage Plant Research
Beverage Plant Research (e-ISSN 2769-2108) is the official journal of Tea Research Institute, Chinese Academy of Agricultural Sciences and China Tea Science Society. Beverage Plant Research is an open access, online-only journal published by Maximum Academic Press which publishing original research, methods, reviews, editorials, and perspectives, which advance the biology, chemistry, processing, and health functions of tea and other important beverage plants.