an ETHYLENE OVERPRODUCER 1-like gene (OsETOL1), modulates differentially drought and submergence tolerance in rice.
- The OsETOL1 transcript was differentially responsive to abiotic stresses. OsETOL1 was found to interact with OsACS2, a homolog of 1-amino-cyclopropane-1-carboxylate (ACC) synthase (ACS), which acts as a rate-limiting enzyme for ethylene biosynthesis.
- OsETOL1 plays distinct roles in drought and submergence tolerance by modulating ethylene production and energy metabolism. Findings from the expression and functional comparison of three ethylene overproducer (ETOL) family members in rice further supported the specific role of OsETOL1 in the responses to the two water stresses.
- OsETOL1 gene may have a negative role in drought tolerance at the reproductive stage. It plays a negative role in ethylene biosynthesis. In a yeast two-hybrid assay, OsETOL1 interacted with OsACS2. The interaction between OsETOL1 and OsACS2 was further confirmed by a bimolecular fluorescence complementation (BiFC) assay in Arabidopsis protoplasts, which indicating that OsETOL1 may function in ACC biosynthesis by interacting with OsACS2 in rice.
- Du et al. propose a simplified model for the distinct roles of OsETOL1 in drought and submergence tolerance (Figure 1):
- Under drought stress at the reproductive stage, the function of OsETOL1 may inhibit the transportation of carbohydrates from leaves to the developing seeds and result in a reduction in grain-filling and spikelet fertility and a delay in ethyleneinduced maturation.
- Under submergence conditions, however, carbohydrate consumption and energy production was promoted by OsETOL1, this change enabled the upper leaves to elongate to extend above the surface of the water.
- The same function of OsETOL1 in modulation of ethylene production caused different morphological alterations in rice under drought and submergence conditions. The OsETOL1-mediated ethylene production and energy metabolism may provide an access to reveal the adaptation strategy to drought and submergence stresses in plants.
GO assignment(s): GO:0005488
Mutants and OE plants:
- osetol1-2 also showed the drought-resistant phenotype. The T-DNA insertion sites of the osetol1-1 and osetol1-2 mutants were located in the third intron and the first exon, respectively.
- Transcript analysis of OsETOL1 suggested that the expression of OsETOL1 was abolished in both the osetol1-1 and osetol1-2 mutants.
- Two allelic mutants of OsETOL1 showed increased resistance to drought stress at the panicle development stage. Interestingly, the mutants exhibited a significantly slower growth rate under submergence stress at both the seedling and panicle development stages.
- Over-expression (OE) of OsETOL1 in rice resulted in reverse phenotypes when compared with the mutants.
- In the osacs2 mutant and OsETOL1-OE plants, ACC and ethylene content were decreased significantly, and exogenous ACC restored the phenotype of osetol1 and OsETOL1-OE to wild-type under submergence stress, implying a negative role for OsETOL1 in ethylene biosynthesis.
- The expression of several genes related to carbohydrate catabolism and fermentation showed significant changes in the osetol1 and OsETOL1-OE plants, implying that OsETOL1 may affect energy metabolism.
- Co-segregation analysis suggested that the drought resistance phenotype was due to the T-DNA insertion in the OsETOL1 gene. The positive effect of OsETOL1-OE on plant growth under submergence conditions may be partially due to the relatively high level of soluble sugar for energy metabolism. In addition, the positive role of OsETOL1 in submergence tolerance may be independent of SNORKEL1/2 and 'SUB1A as these genes are absent in the rice ZH11.
- The OsETOL1 transcript level was strongly induced by drought and ABA, and it was also slightly induced by salt, heat, and ethylene treatments. During submergence treatment, the OsETOL1 transcript was rapidly induced to about seven-fold at 12 h after the initiation of stress, but after this time point the expression declined slowly to the level seen under normal conditions, and it was suppressed after submergence for 5 days.
- The GUS signal in the transgenic rice was strong in the anther, spikelet hull, node, old root, sheaths, and mature leaves by comparison, but the signal was weak in callus, young bud, root, and immature endosperm, a finding that agreed well with the results from the microarray and qPCR.
Green fluorescence produced by OsETOL1-EGFP overlapped with red fluorescence (RFP) produced by 35S: AtAOS–ERFP, suggesting that OsETOL1 is a cytosolic protein.
OsETOL1 is a homolog of the Arabidopsis ETO1 protein that participates in the degradation of type-2 ACS, a ratelimiting enzyme of ethylene biosynthesis. Two additional ETO homologs, OsETOL2 (LOC_Os07g08120) and OsETOL3 (LOC_Os11g37520) showing 73 and 78% identity, respectively, to OsETOL1.
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China
- Du H, Wu N, Cui F, et al. A homolog of ETHYLENE OVERPRODUCER, OsETOL1, differentially modulates drought and submergence tolerance in rice[J]. The Plant Journal, 2014, 78(5): 834-849.
- Wang K L C, Yoshida H, Lurin C, et al. Regulation of ethylene gas biosynthesis by the Arabidopsis ETO1 protein[J]. Nature, 2004, 428(6986): 945-950.