GLK1 plays a positive role in regulating plant tolerance to alkali stress and salt-alkali mixed stress.

The Golden2-like 1 (GLK1) gene regulates photosynthesis and is associated with drought tolerance and cold tolerance. However, no report has determined the role of GLK1 in alkali tolerance. In this study, we found that MsGLK1 responds to alkali and salt-alkali mixed stresses in alfalfa (Medicago sativa) and carried out detailed functional analysis of GLK1 in the model plants Arabidopsis and Medicago truncatula. In Arabidopsis, the atglk1/2 double mutant exhibited reduced tolerance to these two stress treatments compared to the wild type. Conversely, overexpression of MsGLK1 in Arabidopsis displayed enhanced tolerance under the same treatments. To further study the mechanism underlying response to these stresses, we employed the mtglk1 mutant in M. truncatula, a close relative of alfalfa. The mtglk1 mutant suffered severe damage when subjected to the two stresses. Consistent with phenotypic and physiological analyses, 1092 and 999 differentially expressed genes (DEGs) were identified under alkali and salt-alkali mixed stress, respectively. Our results showed that GLK1 plays an important role in regulating tolerance to alkali and salt-alkali mixed stress. A yeast one-hybrid assay revealed that MtGLK1 directly binds to the promoter of the MtMYB-HB-like gene.