A Novel mechanisms of the signaling cascade associated with the SAPK10-bZIP20-NHX1 synergistic interaction to enhance tolerance of plant to abiotic stress in rice (Oryza sativa L.).

The bzip transcription factors can modulate the transcriptional expressions of target genes by binding specifically to cis-regulatory elements in the promoter region of stress-related genes, hence regulating plant stress resistance. Here, we investigated a stress-responsive transcription factor Osbzip20 under abiotic stresses. The OsbZIP20-GFP fusion protein predominantly aggregated in the nucleus, in accordance with our subcellular localization. OsbZIP20 transcript was observed in all vegetative tissues with highest levels being detected in the seed. Transcription of Osbzip20 was induced by salinity, exsiccation, and abscisic acid. Overexpression of OsbZIP20 in transgenic rice considerably improved tolerance to salt and drought stresses, as well as increased sensitivity to ABA. Furthermore, abiotic stress responsive genes transcript were found to be remarkably elevated in transgenic rice overexpressing OsbZIP20 than in wild-type plants. SAPK10 was discovered to directly interact with and phosphorylate OsbZIP20. Yeast one-hybrid and luciferase assay revealed that OsbZIP20 acted as a transcriptional stimulator. Interestingly, gel shift assay showed that phosphorylated bZIP20 augmented its DNA-binding affinity to the ABRE element of the NHX1 promoter and induced its transcription. In sum, our findings establish a novel signaling pathway associated with the SAPK10-bZIP20-NHX1 synergistic interaction, as well as a new strategy for enhancing rice drought and salt tolerance.