Transcriptome-based identification of drought responsive genes in the tea plant

Tea (Camellia sinensis L. (O) Kuntze) is one of the most widely consumed beverages worldwide. Tea growing areas in Kenya often experience drought periods which cause accumulated soil water deficit. These adversely affect tea production and hence necessitate a need to develop drought-adapted tea cultivars that can withstand the stress challenge. Development of such cultivars can be facilitated by better understanding of genetic mechanisms underlying tolerance of the tea plant to water deficit. Tea plants respond to water deficit through poorly understood molecular processes. The present study was therefore, designed with the objective of identifying genes putatively conferring tolerance in the tea plant. Drought tolerant (TRFCA SFS150) and susceptible (AHP S15/10) tea cultivars, both 18-month old, were each separately exposed to water stress or control conditions of 18% and 34% soil moisture content, respectively, for three months in a randomized complete block (RCB) design with three replicates. Fresh shoots (n = 5) were randomly selected and separately harvested from each treatment and replicate. Total RNA of the shoots were extracted, their mRNA reverse transcribed and sequenced on Roche 454 high-throughput pyrosequencing platform. Overall, 232,853 reads were generated. The reads were quality-filtered, trimmed and assembled into 460 long transcripts (contigs). Contigs were annotated using BLAST searches against similar proteins in the Arabidopsis proteome and blast2go against non-redundant database to determine gene ontologies. Drought-related genes including heat shock proteins (HSP70), superoxide dismutase (SOD), catalase (cat), peroxidase (PoX), calmoduline-like protein (Cam7) and galactinol synthase (Gols4) were induced in plants exposed to drought. Additionally, the expressions of HSP70 and SOD were higher in the drought tolerant relative to the susceptible cultivar under drought conditions. Loci with known functional links to physiological and biochemical features of drought response appear to mediate tolerance to drought in C. sinensis. The loci present potential molecular markers for drought tolerance that can be explored through functional genomics to better understand molecular mechanisms underlying drought tolerance in C. sinensis.