Repressed Gene Expression of Photosynthetic Antenna Proteins Associated with Yellow Leaf Variation as Revealed by Bulked Segregant RNA-seq in Tea Plant Camellia sinensis

The young leaves and shoots of albino
tea cultivars are usually characterized
as having a yellow or pale color, high amino acid, and low catechin.
Increasing attention has been paid to albino tea cultivars in recent
years because their tea generally shows high umami and reduced astringency.
However, the genetic mechanism of yellow-leaf variation in albino
tea cultivar has not been elucidated clearly. In this study, bulked
segregant RNA-seq (BSR-seq) was performed on bulked yellow- and green-leaf
hybrid progenies from a leaf color variation population. A total of
359 and 1134 differentially expressed genes (DEGs) were identified
in the yellow and green hybrid bulked groups (Yf vs Gf) and parent plants (Yp vs Gp), respectively.
The significantly smaller number of DEGs in Yf versus Gf than in Yp versus Gp indicated that
individual differences could be reduced within the same hybrid progeny.
Analysis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes
revealed that the photosynthetic antenna protein was most significantly
enriched in either the bulked groups or their parents. Interaction
was found among light-harvesting chlorophyll a/b -binding proteins (LHC), heat shock proteins (HSPs), and
enzymes involved in cuticle formation. Combined with the transcriptomic
expression profile, results showed that the repressed genes encoding
LHC were closely linked to aberrant chloroplast development in yellow-leaf
tea plants. Furthermore, the photoprotection and light stress response
possessed by genes involved in HSP protein interaction and cuticle
formation were discussed. The expression profile of DEGs was verified
via quantitative real-time PCR analysis of the bulked samples and
other F1 individuals. In summary, using BSR-seq on a hybrid
population eliminated certain disturbing effects of genetic background
and individual discrepancy, thereby helping this study to intensively
focus on the key genes controlling leaf color variation in yellow-leaf
tea plants.