Genomic Identification, Evolution, Taxonomy and Expression Analysis of Cell Wall Lignifying <i>DIRIGENT</i> (<i>DIR</i>) <i>PROTEIN</i> Genes Under Drought Stress in <i>Jatropha curcas</i> L.

ABSTRACT Dirigent (DIR) proteins, localised at cell wall, are involved in phenoxy radical coupling reactions during lignin biosynthesis in plant species and provide resistivity against adverse environmental conditions. The sub family distribution of DIR genes are different among plant species. In present study, we genome wide identified 28 DIR domain containing genes in Jatropha curcas . The phylogenetic analysis classified DIR genes into three distinct subfamilies distributed among clades. The taxonomy of DIR genes into three subfamilies were further confirmed via pairwise sequence similarity as ‘lignan‐forming subfamily’ ( DIR ‐a), ‘lignin‐forming subfamily’ ( DIR ‐e) and ‘cell wall signaling subfamily’ ( DIR ‐g). The evolutionary aspects of DIR genes evaluated by divergence analysis further recognised the synonymous and non‐synonymous changes. We have also studied the molecular characterisation of DIR genes within Jatropha genome for its gene structure organisation, the presence of Light responsive, phytohormone responsive, plant growth responsive and stress responsive cis‐regulatory elements in the promotor region, co‐expression network with lignin biosynthesis genes, and predicted miRNA target sites, regulated by miRNA mediated post transcriptional regulatory network. Moreover, the biological process enrichment based on gene ontology further revealed the involvement of DIR genes in biosynthetic process of phenylpropanoid and organic substance as well as cellular metabolic process. Subsequently, the co‐occurrence of DIR genes with streptophyta taxa's was confirmed mostly in eukaryota. Furthermore, the expression profiles of DIR genes in different tissues of Jatropha under drought stress exhibited significant differential expression. This study provide basis for functional divergence of DIR genes in lignifying plant cell wall and providing protection against environmental stresses in plants.