RESUMO
Mitogen-activated protein kinase kinase kinases (MAPKKKs) are important components of the MAPK cascade and play crucial roles in development and stress responses. Arabidopsis pumila is an ephemeral Brassicaceae plant growing in Xinjiang desert regions, which possesses salt tolerance. To explore the evolution and function of the MAPKKK gene family in A. pumila, 143 ApMAPKKK genes were identified from A. pumila genome by genome-wide analysis, which were categorized into three subfamilies: ZIK (20), MEKK (36) and RAF (87). There existed 74 and 72 colinear genes between A. thaliana, A. lyrata and A. pumila, respectively, indicating that this gene family expanded obviously in A. pumila genome. Evolutionary analysis revealed that there were 64 duplicated gene pairs with Ka/Ks less than 1, and purifying selection was dominant. RNA-seq data were used to analyze the expression characteristics of ApMAPKKK genes in response to salt stress and in different tissues. The results showed that most ApMAPKKK genes were up-regulated under 250 mmol/L NaCl stress. For example, ApMAPKKK18-1/2 and ApMAPKKK17-1/2 were substantially up-regulated. Tissue expression profiles showed that ApMAPKKK mainly presented six expression patterns. Some duplicated genes were differentially expressed in response to salt stress and in different tissues. These results lay a foundation for further understanding the complex mechanism of MAPKKK gene family transduction pathway in response to abiotic stresses in A. pumila.