From Chloroplast Biogenesis to Chlorophyll Accumulation: The Interplay of Light and Hormones on Gene Expression in Camellia sinensis cv. Shuchazao Leaves

Abstract

Chloroplast development and chlorophyll metabolism have been well described in model plants but not in perennial woody crops. Of particular interest is the interplay between light and hormones under shade conditions. We report that the shade induced accumulation of chlorophylls in Camellia sinensis cv. Shuchazao leaves is at least as a result of (a) positive changes in chloroplast development and (b) light/hormonal regulation of genes and transcription factors involved in the chlorophyll biosynthesis pathway. Under shade conditions, leaves developed an abundance of enlarged chloroplasts encapsulating more prominent thylakoid membranes. Four major metabolites in the chlorophyll biosynthesis pathway namely Chl a, Chl b, DPP, and Mg-Proto IX increased under shade conditions while PBG decreased significantly. Significant changes were found at the transcription level of regulators of chloroplast biogenesis (GLK1 and LHCB), the structural genes in the chlorophyll biosynthesis pathway (HEMA1, CLH1, PORA, and CAO) and potential components involved in light signaling (PHYA, CRY1, HY5, and DELLAs). Two central signal integrators (GLK1 and LHCB) between the nucleus and chloroplast showed clear responses to shade, suggesting a crucial role of light in regulating chloroplast development in tea leaves. Concurrent with the changes in gene expression, the concentrations of endogenous phytohormones (auxin, cytokinin, and gibberellins) increased significantly in the later stages of shade conditions. Two key integrators involved in the hormone signal pathways, EIN3 and EBF1/2, increased under shade conditions suggesting that shade induced changes to hormone levels may play some role in modulating chlorophyll biosynthesis in the tea leaves. Overall, this data suggests that the light and hormone influence over chloroplast development and chlorophyll biosynthesis in Camellia is similar to that of Arabidopsis. This study provides new insights into the molecular mechanisms that regulate chlorophyll biosynthesis in response to light and hormones in a commercially important woody plant such as Camellia, which may facilitate the breeding of high-chlorophyll tea cultivars for the improvement of sensory features of the green tea product.

Dark-Induced Hormonal Regulation of Plant Growth and Development

“…Thus, the PIF-HY5 regulatory mechanism is crucial for the proplastid development. Golden2-Like (GLK) nuclear TFs which work independently of phytochromes and PIFs are also the key regulators of plastid biogenesis ( Liu et al, 2020 ). GLKs strongly activate the chlorophyll biosynthesis enzymes and light-harvesting chlorophyll binding proteins including, GlutRNA reductase (HEMA1), magnesium chelatase (CHLH), pchlide oxidoreductase (POR-B) and chlidea oxygenase (CAO).…”

HAK/KUP/KT family potassium transporter genes are involved in potassium deficiency and stress responses in tea plants (Camellia sinensis L.): expression and functional analysis

“…Among these substances, catechins, theanine, and caffeine are the most important characteristic secondary metabolites in tea bud and leaf, which endow the tea with a rich taste and many health benefits [ 1 – 3 ]. Generally, the composition of the tea bud and young leaf is greatly influenced by many factors, such as the tea plant cultivar, nutrition status and environmental factors [ 4 – 7 ]. Out of these factors, mineral nutrition, especially nutrition of potassium, considerably affects the growth and development of tea plants [ 8 ].…”

Phenotypic Markers Reflecting the Status of Overstressed Tea Plants Subjected to Repeated Shade Cultivation

“…Shade cultivation, a traditional Japanese tea cultivation system, is used to produce high-quality Japanese green tea products, such as Matcha and Gyokuro. Shading markedly changes the phenotypes of tea plants, especially leaf color, which becomes dark green because of chloroplast enlargement, increased chlorophyll content, and up-regulation of genes involved in the chlorophyll biosynthesis pathway in response to limited sunlight (Sano et al, 2018;Liu et al, 2020). Limiting irradiation substantially stresses plant growth, and repeated shading of tea plants potentially reduces their health.…”