High-Light-Induced Degradation of Photosystem II Subunits’ Involvement in the Albino Phenotype in Tea Plants

Abstract

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar “Huangjinya” (HJY), with a normal green-leaf cultivar “Jinxuan” (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll–protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant.

Shading-Dependent Greening Process of the Leaves in the Light-Sensitive Albino Tea Plant ‘Huangjinya’: Possible Involvement of the Light-Harvesting Complex II Subunit of Photosystem II in the Phenotypic Characteristic

“…However, numerous DEGs belonged to the photosynthesis-related pathways although the content of photosynthetic pigments also increased in the shaded leaves of ‘HJY’ [ 8 ]. Furthermore, high light exposure had been found to accelerate the depolymerization of PSII complex subunits such as CP43, CP47, PsbP, and PsbR, resulting in the degradation of the reaction center proteins D1 and D2 [ 13 ]. These findings suggested that the albino phenotype of tea plants might be closely associated with the abnormal assembly of the photosynthesis-related proteins in addition to the lack of pigments [ 9 , 23 ].…”

“…Similar inhibition of the chlorophyll biosynthesis had also been witnessed in light-sensitive albino cultivars ‘Zhonghuang 2#′ [ 11 ]. In the albino leaves of the ‘Huangjinya’, the expressions of the genes encoding the photosystem II (PSII) complex subunits and light-harvesting complex (LHC) subunits were remarkably suppressed [ 7 ], which would inhibit the accumulation of the CP43 and CP47, consequently accelerate the degradation of D1 and D2 [ 13 ], and finally induce the collapse of photosynthesis. Comparison between the albino leaves and re-greened ones of the ‘Huangjinya’ showed that the differentially expressed genes (DEGs) were highly enriched in the pathways of photosynthesis and the photosynthetic antenna proteins [ 14 ].…”

Metabolic and Transcriptomic Profiling Reveals Etiolated Mechanism in Huangyu Tea (Camellia sinensis) Leaves

“…Eventually it leads to a decrease in chlorophyll concentration or the albino phenotype. Interestingly, these processes are reversible, and it leads to adaptations to high-light stress in the etiolated tea mutant [ 58 ].…”

Exploring the RNA Editing Events and Their Potential Regulatory Roles in Tea Plant (Camellia sinensis L.)

“…However, a recent study noted that using the second, fifth and last amino acids of the PPR motif to predict downstream target sequences containing RNA editing sites would obtain more accurate results [ 51 ]. An absence of RNA editing can cause albino leaves and etiolation in some Arabidopsis and rice mutants, such as atclb19 , osppr6 , osdua1 and atgun1 [ 12 , 13 , 30 , 52 ], and many albino and etiolation varieties of tea plants have been bred [ 32 ], such as Baiye 1, Huabai 1, Huangjinya, etc. However, whether the extent of RNA editing is affected by the color change of tea leaves remains unclear.…”

“…In China, many albino and etiolation tea cultivars, such as ‘Baiye 1’, ‘Huangjinya’, ‘Huabai 1’ and ’Baijiguan’ [ 32 , 33 , 34 ], attract more attention due to their umami taste, lower astringency and higher economic and ornamental value [ 35 ]. Numerous studies reported that loss of the RNA editing function could lead to changes in plant leaf color [ 12 , 30 ].…”