Genome-Wide Identification of the <i>MPK</i> Gene Family and Expression Analysis under Low-Temperature Stress in the Banana

Mitogen-activated protein kinases (MAPKs and MPKs) are important in the process of resisting plant stress. In this study, 21, 12, 18, 16, and 10 <i>MPKs</i> were identified from <i>Musa acuminata</i>, <i>Musa balbisiana</i>, <i>Musa itinerans</i>, <i>Musa schizocarpa</i>, and <i>Musa textilis</i>, respectively. These <i>MPKs</i> were divided into Group A, B, C, and D. Phylogenetic analysis revealed that this difference in number was due to the gene shrinkage of the Group B subfamily of <i>Musa balbisiana</i> and <i>Musa textilis</i>. KEGG annotations revealed that K14512, which is involved in plant hormone signal transduction and the plant–pathogen interaction, was the most conserved pathway of the <i>MPKs</i>. The results of promoter cis-acting element prediction and <i>foc</i>TR4 (<i>Fusarium oxysporum</i> f. sp. <i>cubense</i> tropical race 4) transcriptome expression analysis preliminarily confirmed that <i>MPKs</i> were relevant to plant hormone and biotic stress, respectively. The expression of <i>MPKs</i> in Group A was significantly upregulated at 4 °C, and dramatically, the <i>MPKs</i> in the root were affected by low temperature. miR172, miR319, miR395, miR398, and miR399 may be the miRNAs that regulate <i>MPKs</i> during low-temperature stress, with miR172 being the most critical. miRNA prediction and qRT-PCR results indicated that miR172 may negatively regulate <i>MPKs</i>. Therefore, we deduced that <i>MPKs</i> might coordinate with miR172 to participate in the process of the resistance to low-temperature stress in the roots of the banana. This study will provide a theoretical basis for further analysis of the mechanism of <i>MPKs</i> under low-temperature stress of bananas, and this study could be applied to molecular breeding of bananas in the future.