De Novo Transcriptome Assembly and Identification of Brassinosteroid Biosynthetic Pathway in Safflower

Safflower (Carthamus tinctorius L.) is known for its oil quality and ability to grow in drought conditions. The threat to global food security posed by challenges of climate change has stressed the use of functional genomics in current plant breeding approaches. Plant steroid hormones called brassinosteroids (BRs) are at the nexus of regulating plant growth and development, and plant stress responses. Enhanced BR levels or signalling have increased crop yields by up to 40% while also conferring broad range stress tolerance. Currently there is no information on the BR biosynthesis and signalling pathways in safflower. A de novo transcriptomic analysis of untreated and 24-epibrassinolide (EBR)-treated safflower leaves was conducted using the Illumina sequencing platform. Approximately 5 GB clean data were generated from untreated and EBR-treated samples that assembled into 34,456 and 36,997 transcripts (combined 50,630), and 30,180 and 32,333 CoDing sequences (CDS) (combined 43,637), respectively. More than 71% of the CDS were annotated with majority of hits against Cynara cardunculus var. scolymus, a thistle in the safflower family. A total of 74 KEGG pathways were identified in safflower. Six genes, including DWF4 that codes for a rate-limiting enzyme in BR biosynthesis, were mapped to the BR biosynthesis pathway using the KEGG mapper.