Exploitation of Hi-C sequencing for improvement of genome assembly and in-vitro validation of differentially expressing genes in Jatropha curcas L.

Jatropha curcas is one of the major sources of renewable energy due to potential use of its oil as a biofuel. The genome of this crop is constituted by the high content of repetitive elements. We employed the Hi-C proximity ligation technique to re-scaffold our existing hybrid genome assembly of an elite genotype (RJC1) developed using Illumina and Pacbio technologies. We assembled 99.81% of non-truncated reads to achieve 266.80 Mbp of the genome with an N50 value of 1.58 Mb. Furthermore, we compared the efficiency of Hi-C-augmented genome assembly with the hybrid genome assembly and observed a ~ 50% reduction in scaffolds and a tenfold increase in the N50 value. The gene ontology analysis revealed the identification of terms for molecular function (45.52%), cellular component (33.47%), and biological function (20.99%). Comparative genomic analysis of 13-plant species showed the conservation of 414 lipid metabolizing genes identified in the KEGG pathway analysis. Differential gene expression (DGE) studies were conducted in the healthy and Jatropha mosaic virus-infected leaves via RNA-seq analysis and observed gene expression changes for 2185 genes. Out of these, we observed 546 genes having more than two-fold change of transcript level and among these 259 genes were down-regulated and 287 genes were up-regulated. To validate RNA-seq data, two DEGs were selected for gene expression analysis using qRT-PCR and the data was in correlation with in silico results. RNA-seq analysis further shows the identification of some of the candidate genes and may be useful to develop JMV resistant plants after functional validation. This Hi-C genome assembly provides a detailed accurate reference genome which could be utilized to improve Jatropha and other economically important Euphorbiaceae family members. © King Abdulaziz City for Science and Technology 2020.