Comprehensive Transcriptomic Analysis of the Wild Plant Species Calotropis procera in Response to Water Irrigation

Calotropis procera is a desert flowering plant in the dogbane family (Apocynaceae) native to North Africa, Tropical Africa, Western Asia, South Asia, and Indochina. It is widely used in traditional medicinal uses. C. procera has been shown to withstand arid conditions and maintain high rates of photosynthesis. In this study, we seek to understand the molecular mechanisms by which C. procera tolerates drought. We performed a transcriptomic profiling of the plant leaves at three time points; one hour after dawn, midday, and one hour before sunset. All three-time points were collected before and after irrigation. We pooled about 400 million paired end fragments of illumina RNAseq for de novo assembly of C. procera transcriptome using Trinity software.  The final assembly has 89838 ESTs with contig N50 of 1614 bp. Expression abundance was assessed by an express software followed by exclusion of low abundant ESTs (<10 FPKM in all samples). Subsequent differential expression analysis was done using EdgeR package. ANOVA of the two-time series showed significance at 3 < fold change (p value < 0.001) for 275 Arabidopsis matched ESTs across one day before irrigation and 1210 Arabidopsis matched ESTs in the irrigation day. Interaction between the irrigated and the non-irrigated conditions is 229 ESTs. Pathway enrichment analysis using Arabidopsis orthologs revealed a role of phenylpropanoid metabolism in response to sun light and water availability. Further analyses to detect other drought-related genes and metabolic pathways are underway.