Acireductone dioxygenase (ARD) is a metal-binding metalloenzyme and involved in the methionine salvage pathway.

In rice, OsARD1 binds Fe2+ and catalyzes the formation of 2-keto-4-methylthiobutyrate (KMTB) to produce methionine, which is an initial substrate in ethylene synthesis pathway. Here, we report that overexpression of OsARD1 elevates the endogenous ethylene release rate, enhances the tolerance to submergence stress, and reduces the sensitivity to drought, salt, and osmotic stresses in rice. OsARD1 is strongly induced by submergence, drought, salinity, PEG6000, and mechanical damage stresses and exhibits high expression level in senescent leaves. Transgenic plants overexpressing OsARD1 (OsARD1-OE) display fast elongation growth to escape submergence stress. The ethylene content is significantly maximized in OsARD1-OE plants compared with the wide type. OsARD1-OE plants display increased shoot elongation and inhibition of root elongation under the submergence stress and grow in dark due to increase of ethylene. The elongation of coleoptile under anaerobic germination is also significantly promoted in OsARD1-OE lines due to the increase of ethylene content. The sensitivity to drought and salt stresses is reduced in OsARD1-OE transgenic lines. Water holding capacity is enhanced, and the stomata and trichomes on leaves increase in OsARD1-OE lines. Drought and salt tolerance and ethylene synthesis-related genes are upregulated in OsARD1-OE plants. Subcellular localization shows that OsARD1 displays strong localization signal in cell nucleus, suggesting OsARD1 may interact with the transcription factors. Taken together, the results provide the understanding of the function of OsARD1 in ethylene synthesis and abiotic stress response in rice.





Figure 1: Expression patterns of OsARD1(AJ) GUS staining in different tissues and organs. (A) Seedling in tissue culture. (B) Root. (C) Root tip. (D) Leaf sheath with ligule and auricle. (E) Leaf blade. (F) Stem. (G) Callus. (H) Floral. (I) 2-cm-long young panicle, arrowhead is intercalary meristem. (J) 22-cm-long panicle. (KM) The section of GUS expression in root tip. (K) Longitudinal section. (LM) Cross section, arrowhead is meristematic cell of lateral-root primordial. (N) qRT-PCR analysis of OsARD1 expression in different organs. Panicle 1: 0.3–0.5-cm young panicles, panicle 2: 1–2-cm young panicles, panicle 3: 3–4-cm young panicles, panicle 4: 5–6-cm young panicles, panicle 5: 10–11-cm young panicles, panicle 6: panicle at heading stage. (O) qRT-PCR analysis of OsARD1 expression at different developmental stages. OsActin1 was used as an internal control for the relative quantification of target gene expression in qRT-PCR. Scale bars: 0.5 cm for AJ and 100 μm for KM.