The GRAS transcription factor OsGRAS2 negatively impacts salt tolerance in rice

Transcription factor OsGRAS2 regulates salt stress tolerance and yield in rice. Plant-specific GRAS transcription factors are involved in many different aspects of plant growth and development, as well as in biotic and abiotic stress responses, although whether and how they participate in salt stress tolerance in rice (Oryza sativa) remains unclear. A screen of a previously generated set of activation-tagged lines revealed that Activation Tagging Line 63 (AC63) displayed a salt stress-sensitive phenotype. Subsequent thermal asymmetric interlace polymerase chain reaction (TAIL-PCR) showed that AC63 was due to overexpression of OsGRAS2. Ectopic overexpression of OsGRAS2 caused increased salt stress sensitivity, while osgras2 loss-of-function lines displayed salt stress-resistant phenotypes. Further, we observed that OsGRAS2 impacts Na⁺ and K⁺ ion homeostasis in the shoots. Mutation of OsGRAS2 increased salt tolerance without yield penalty. Phylogenetic tree analysis indicated that OsGRAS2 belonged to the LISCL subfamily of GRAS transcription factors and had high amino acid similarity to OsGRAS23. Both OsGRAS2 and OsGRAS23 underwent homomeric and heteromeric interactions, indicating that they formed homo- and hetero-dimers. Moreover, OsGRAS2 and OsGRAS23 showed transcriptional activation activity that was mostly governed by motif1, which was located at the N-terminal region. Further, we found OsGRAS2 binds to the OsWRKY53 promoter to increase its expression, thereby negatively impacting the OsHKT1;5 expression. This study demonstrates a novel insight into how LISCL subfamily GRAS transcription factors impact salt stress tolerance in rice.