Molecular Basis of the Distinct Metabolic Features in Shoot Tips and Roots of Tea Plants (Camellia sinensis): Characterization of MYB Regulator for Root Theanine Synthesis

The physiological and metabolic differences
between shoot tips
and roots of tea plants are significant, and understanding them is
required for improvement of tea quality and plant growth. A high-quality
full-length transcriptome sequencing on tea plant roots and shoot
tips by PacBio SMRT technology was done to gain a further understanding.
Approximately 160699 and 166120 full-length transcripts were recovered
in roots and shoots, respectively, including 31232 and 41068 novel
isoforms and 16960 and 26029 alternative splicing (AS) isoforms. These
supported 21699 full-length reads and 31232 and 41068 novel transcripts
from root and shoot, respectively, including 1679 long noncoding RNAs
(lncRNAs) and 2772 fusion transcripts, which significantly upgrade
the Camellia sinensis genome annotation.
The respective 6475 and 6981 transcripts in roots and shoots differ
in 3′-untranslated regions. Meanwhile, extensive analyses of
novel transcripts, ASs, and lncRNAs also revealed a large number of
ASs and lincRNAs closely related to the regulation of characteristic
secondary metabolites including catechins, theanine, and caffeine.
Finally, a root-specific CsMYB6 was characterized
to regulate theanine biosynthesis by genetic and molecular analyses.
CsMYB6 directly bound to and activate the promoter of theanine
synthetase gene (CsTSI). The study lays
a foundation for the further investigation of metabolic genomics and
regulation in tea plants.