**5. Conclusions**

Kiwifruit (*Actinidia chinensis*) has become an important commercial fruit due to its pleasant flavor and nutritional components that benefit human health [39]. However, research progress on kiwifruit has been relatively slow compared to grape and apple horticultural crops. MAPK cascade is one of the major pathways in plants, with MAPK as the downstream molecule of the MAPK cascade playing an important role in singling [6]. In this study, we identified 18 putative *MAPK* genes from the kiwifruit genome and established their classification and phylogenetic relationships, gene structure, conserved protein domains/motifs, and promoter regions. The phylogenetic relationship of MAPKs among kiwifruit demonstrated that the 18 *AcMAPK* genes were grouped into five subgroups (A, B, C, D, and E), and most genes within the same group generally share similar exon/intron patterns and conserved protein domains and motifs. Our analyses strongly supported the identity of each subgroup. The expression profiles of the MAPK cascade genes in various biotic and abiotic stresses and hormones treatments were discussed. The majority of the MAPK cascade genes could be induced by one or more specific treatments. In summary, our study provides an overview of the *MAPK* gene family in kiwifruit, which will be helpful in the biochemical functional characterization of the MAPK cascades in kiwifruit.

**Supplementary Materials:** Supplementary materials can be found at http://www.mdpi.com/1422-0067/19/9/2510/ s1.

**Author Contributions:** G.W. and J.-Y.Z. designed and initiated this study. G.W. and Z.-H.J. carried out the bioinformatics analyses. G.W. and D.-L.P. performed the qRT-PCR experiments. G.W. and J.-Y.Z. wrote the manuscript. T.W., J.-P.X. and Z.-R.G. helped in discussions of the manuscript. All authors read and approved the final manuscript.

**Acknowledgments:** This research is supported by the Natural Science Foundation of Jiangsu Province of China (General Program, BK20171328).

**Conflicts of Interest:** The authors declare no conflict of interest.
