The Glycine Max Abscisic Acid-Activated Protein Kinase-Like Kinase 1 (GmAALK1) Modulates Drought Stress Response

Abscisic acid-activated protein kinases (AAPK) are key components in abscisic acid (ABA) signalling and have been implicated in mediating responses to abiotic stresses in plants. However, the mechanistic involvement of AAPK genes in drought stress responses has not been functionally characterized to date in soybean. In this study, we identified Glycine max AAPK-like kinase (GmAALK) genes. Loss-of-function analysis of GmAALK1 in soybean reveal that GmAALK1-RNAi plants are more drought-susceptible than pRAP17-ccdB control lines under drought stress. In contrast, GmAALK1 overexpression lines show enhanced drought resistance under drought stress as compared to pRAP15-ccdB control plants. A root transcriptome analysis reveals the differential expression of many genes related to physiological and biochemical changes in GmAALK1-RNAi plants when compared with the pRAP17-ccdB control plants with or without drought stress. Twelve candidate drought-responsive, differentially-expressed genes have been selected to understand the role of GmAALK1 in during the drought response. Gene expression analyses revealed that GmAALK1 positively modulates the drought stress response. These studies suggest that GmAALK1 overexpressing roots increase the transcription of ABA-responsive genes, indicating that the GmAALK1 is a positive regulator of ABA-mediated stress-signaling pathways in soybean. The phylogenetic and domain analyses also support that GmAALK1 is an AAPK and that it has a role in the drought response. These results provide a genetic foundation for developing drought-tolerant soybean cultivars via manipulating kinase gene family which will be applicable to additional cultivated crops experiencing drought conditions relating to climate change.