The mitogen-activated protein kinase kinase MKK2 positively regulates constitutive cold resistance in the potato

Abstract

Cold stress is a detrimental environmental factor affecting plant growth and development. The mitogen-activated protein kinase (MAPK) cascade pathway mediates various signalling pathways associated with abiotic stress tolerance in plants. In this research, 15 MAPKs, 5 MAPKKs and 83 MAPKKKs in the potato genome were identified by comparative genomics analysis and named following the Arabidopsis MAPK nomenclature model. The differentially expressed genes in response to cold stress between S. acaule and S. tuberosum were enriched in the MAPK cascade pathway. Quantitative real-time PCR (qRT-PCR) results revealed that the expression of SaMKK2 and SaMAPK16 particularly increased in the cold-tolerant S. acaule. Additionally, the promoters of StMKK2 and SaMKK2 differ largely in cold responsive motifs. Compared with wild-type E3, transgenic lines overexpressing SaMKK2 exhibited dramatic improvement of constitutive cold resistance in the potato, indicating that the function of MKK2 is species-dependent. However, SaMAPK16 overexpression had no effects on either cold resistance without or with cold acclimation. Furthermore, the transcriptome and qRT-PCR data showed that overexpression of SaMKK2 led to a significant increase in the expression of CBF1/2/3, OPR2 and SLD2 after cold treatment for two hours compared with wild-type under cold stress. The results of yeast two-hybrid and bimolecular fluorescence complementation experiments together suggested that SaMKK2 interacted with SaMAPK4/7 and that the interaction occurred in the cytoplasm. Given these results, we concluded that the interaction between SaMKK2 and SaMAPK4/7 may positively promote the expression of CBFs, OPR2 and SLD2, which eventually increases the constitutive cold resistance of potato.