A homolog of ETHYLENE OVERPRODUCER, OsETOL1, differentially modulates drought and submergence tolerance in rice

Submergence and drought are major limiting factors for crop production. However, very limited studies have been reported on the distinct or overlapping mechanisms of plants in response to the two water extremes. Here we report an ETHYLENE OVERPRODUCER 1-like gene (OsETOL1) that modulates differentially drought and submergence tolerance in rice (Oryza sativa L.). 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. 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. 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. These results together suggest that 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.