Genome-wide Identification of Jatropha curcas MAPK, MAPKK, and MAPKKK Gene Families and Their Expression Profile Under Cold Stress

Mitogen-activated protein kinase (MAPK) cascades are fundamental signal transduction modules in all eukaryotic organisms, controlling cell division, growth, development, and hormone signaling. Additionally, they can be activated in response to a variety of biotic and abiotic stressors. Although the evolution and expression patterns of MAPK cascade families have been systematically investigated in several model plants (e.g., Arabidopsis, rice, and poplar), we still know very little about MAPK, MAPKK, and MAPKKK families in Jatropha curcas, an economically important species. Therefore, this study performed genome-wide identification and transcriptional expression analysis of these three families in J. curcas. We identified 12 J. curcas MAPK (JcMAPKs), 5 JcMAPKKs, and 65 JcMAPKKKs. Phylogenetic analysis classified all JcMAPKs and JcMAPKKs into four subgroups, whereas JcMAPKKKs were grouped into three subfamilies (MEKK, RAF, and ZIK). Similarities in exon/intron structures supported the evolutionary relationships within subgroups and subfamilies. Conserved motif analysis indicated that all J. curcas MAPK cascades possessed typical, 200-300 amino-acid protein kinase domains. MAPK cascade genes were presented throughout all 11 chromosomes. Gene duplication analysis suggested that after JcMAPK and JcMAPKKK diverged, 3 and 19 tandem duplicates occurred under strong purifying selection. Furthermore, RNA-seq and qRT-PCR analyses revealed that some MAPK cascade genes are predominantly expressed in specific tissues. Moreover, their expression levels significantly increased under cold treatment. Our results should provide insight into the roles of MAPK cascade genes in regulating J. curcas stress responses and in hormonal signal transduction. Furthermore, these data have important applications in the genetic improvement of J. curcas.