StMAPKK1 enhances drought and salt tolerance in potato via ROS scavenging and stomatal closure.

Drought and salt stress are among the main factors affecting agricultural productivity, seriously influencing the growth, development and yield of potatoes. The mitogen-activated protein kinase (MAPK) cascade is highly conserved in signal transduction under abiotic stress. However, studies on the expression patterns of the mitogen-activated protein kinase kinase (MAPKKs) gene under drought and salt stress are limited, and there is a lack of functional verification of it in supporting potato plant growth. The expression pattern of StMAPKK family genes in potato plants was analyzed by qRT-PCR method. StMAPKK1 was identified as a drought-tolerant and salt-tolerant gene, which showed significant upregulation under drought and salt (200 mM NaCl) stress. Subcellular localization shows that it is expressed in the nucleus and cell membrane. To verify its function, we constructed overexpressing and knocking down expression plants. Under drought and salt stress, the transgenic lines overexpressing StMAPKK1 showed increased antioxidant enzyme activity, increased proline content and decreased malondialdehyde content, indicating that the redox homeostasis in the overexpressing plants was improved. The expression of key antioxidant response genes (StSOD1, StSOD2, StPOD12, StPOD47, StPOD66, StCAT1 and StCAT2) and drought and salt-tolerant StMAPK genes (StMAPK3 and StMAPK10) in overexpressed plants was upregulated. The enzyme defense system and MAPK cascade amplification signal were enhanced, improving drought and salt tolerance. Overexpressed plants also enhanced photosynthesis, stomata closed, and reduced water transpiration. Confirm the positive role of StMAPKK1 in drought resistance and salt tolerance. On the contrary, the results in the knocking down expression plants were opposite to those in the overexpression plants. These findings highlight that StMAPKK1, as a key factor in the MAPK cascade reaction, plays a positive regulatory role in the drought and salt tolerance of potatoes.