Constitutive Overexpression of the Della-Like Gene Zpr31 From Zygophyllum Potaninii Maxim Suppresses the Antioxidant Response of Arabidopsis Thaliana Under Mannitol-Induced Osmotic Stress

ZpR31, a DELLA-like transcript whose deduced protein shares sequence similarity with GAI1, was previously identified by suppression subtractive hybridization (SSH) as downregulated in mannitol-stressed Zygophyllum potaninii. To characterise its function, transgenic Arabidopsis thaliana lines constitutively overexpressing ZpR31 (ZpR31-OE) were generated and, together with wild-type (WT) Col-0 plants, exposed to 200 mM mannitol. After 15 days of treatment, malondialdehyde (MDA) content was markedly higher in two independent ZpR31-OE lines (approximately 23–32 nmol g‑1) than in WT (approximately 16.5 nmol g‑1), indicating more extensive membrane lipid peroxidation. Superoxide dismutase (SOD) activity increased markedly in stressed WT (from approximately 410 to 515 U g‑1), whereas it declined to approximately 210 U g‑1 in both ZpR31-OE lines. Stem-loop RT-qPCR of six stress-associated microRNAs in ZpR31-OE plants relative to WT revealed transient induction of miR156, miR165, miR398 and miR827 at 24 h, a delayed miR393 peak at 48 h, and sustained miR171 repression. Because miR398 is normally downregulated under oxidative stress to permit induction of Cu/Zn-SOD genes, its induction here suggests a plausible mechanism by which ZpR31 suppresses the SOD response. These results indicate that ZpR31 acts as a negative regulator of osmotic-stress tolerance in Arabidopsis, consistent with its identification as a stress-downregulated transcript in native Z. potaninii.