Modulation of JA–GA signaling and drought response by a truncated OsJAZ9 protein in rice

Plant growth and stress regulation are tightly regulated by phytohormone signals which are jasmonic acid (JA) and gibberellic acid (GA). Antagonistic crosstalk between JA and GA signaling pathways is mediated by repressor proteins, including JASMONATE ZIM-DOMAIN PROTEINs (JAZ) in the JA and DELLA proteins in the GA. In rice (<i>Oryza sativa</i>), the interaction between OsJAZ9 and rice DELLA protein SLENDER RICE 1 (SLR1) has been identified as a key role in the antagonistic interplay between JA and GA.In this study, we generated transgenic rice lines constitutively overexpressing a truncated form of OsJAZ9 that retains the <i>N</i>-terminal ZIM domain but lacks the C-terminal Jas domain (OsJAZ9NZ-OE). We hypothesized that this construct could alter JAZ-DELLA interactions and thereby affect both JA- and GA-associated processes. OsJAZ9NZ-OE plants displayed increased plant height and improved recovery under drought stress. At the transcriptional level, <i>OsbHLH148</i> and <i>OsMYC2</i> (JA-associated) and <i>OsWRKY71</i> (ABA/stress-associated), and the GA-related transcription factors <i>OsPIL14</i> and <i>OsPIL15</i> were all upregulated, indicating that OsJAZ9NZ influences a broad set of hormone-responsive pathways that coordinate growth and stress responses.These findings indicate that structural modification of OsJAZ9 alters JA-GA signaling balance and is associated with transcriptional reprogramming that affects both growth and drought tolerance. While further work is required to clarify the underlying mechanisms, OsJAZ9NZ provides a useful genetic tool to probe hormone crosstalk and may represent a promising genetic resource for crop improvement under environmental stress.