Known as crucial positive regulators of abscisic acid (ABA) and osmotic stress responses Arabidopsis thaliana and rice, SNF 1-RELATED PROTEIN KINASE 2 (SnRK2) plays important roles in various processes. Osmotic stress/ABA–activated protein kinases 2 (SAPK 2) is a member of SnRK2 subclass II in rice. However, little information is available regarding the functional properties of rice SAPK2.
Prof. YU Diqiu and his team of Xishuangbanna Tropical Botanical Garden (XTBG) used the CRISPR/Cas9 system to generate sapk2 mutants. They characterized the functional properties of SAPK2 by developing loss-of-function mutants.
Expression analyses revealed that SAPK2 expression was strongly induced by drought, NaCl, and polyethylene glycol (PEG) treatments, but not by ABA. The results imply that SAPK2 has a significant role in the ABA signaling pathway during the initial development stages in rice.
Germination assays proved that the sapk2 mutants exhibited an ABA-insensitive phenotype during the germination and post-germination stages. Drought tolerance assays indicated that sapk2 mutant lines were sensitive to drought conditions, with lower survival rates than the wide-type plants.
The mutants also exhibited greater water loss, lower proline and soluble sugar contents, higher proportions of fully open stomata, higher ROS levels, and lower antioxidant enzyme activities.
Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analyses indicated that SAPK2 improved drought tolerance by enhancing the expression of stress-responsive and antioxidant enzyme genes in rice.
The researchers also observed that SAPK2 increased the tolerance of rice to salt and PEG stresses.
The research results confirmed that SAPK2 was an important positive regulator of ABA-dependent abiotic stress responses and developmental controls in rice.