Overexpression of the cassava (Manihot esculenta) PP2C26 gene decreases drought tolerance and abscisic acid responses in transgenic Arabidopsis thaliana

Background: Cassava (Manihot esculenta Crantz) stands as a pivotal food crop within tropical and subtropical regions. With its inherent drought-tolerant traits, cassava proves to be an ideal candidate for investigating drought tolerance mechanisms in staple crops. Although protein phosphatase 2C (PP2Cs) plays a critical role in drought stress responses in plants, the molecular mechanism of PP2Cs in cassava has yet to be elucidated. Results: In this research, we cloned MePP2C26, a member of group A PP2Cs, which exhibited significant upregulation following treatments with mannitol, NaCl, and ABA. Arabidopsis transgenic lines overexpressing MePP2C26 exhibited reduced drought tolerance, with survival rates of 39 %, 37 %, and 39 % for OV2, OV3, and OV6 lines, respectively, compared to 53 % in wild-type (WT) and 52 % in vector control (VC) plants. Additionally, these transgenic lines showed altered responses to exogenous ABA, as MePP2C26 overexpression significantly alleviated ABA-induced inhibition of seed germination and root growth. These lines displayed elevated levels of malondialdehyde (MDA), ion leakage (IL), and reactive oxygen species (ROS), accompanied by reduced activities of catalase (CAT) and peroxidase (POD) as well as decreased proline accumulation compared to the wild type (WT) under drought stress conditions. Furthermore, MePP2C26 was shown to downregulate the expression of genes involved in the ABA signaling pathway (including AtSnRK2.6, ABF2, ABF3, RD26, and RD29B) under drought conditions, as evidenced by the transgenic line exhibiting consistently lower expression levels of these genes (despite their drought-induced upregulation in both transgenic and wild-type plants) compared to the WT. MePP2C26 was found to be localized in the nucleus and exhibited self-activation. Moreover, a number of MePYLs (MePYL1, MePYL4-9, MePYL11-13) were found to interact with MePP2C26 in the presence or absence of ABA. Conclusions: In conclusion, the results of this study indicate that MePP2C26 acts as a negative regulator in both drought tolerance and ABA signaling pathways in Arabidopsis.