Cloning and characterization of AKR4C14, a rice aldo-keto reductase, from Thai Jasmine rice

Aldo-keto reductase (AKR) is an enzyme superfamily whose members are involved in the metabolism of aldehydes/ketones. The AKR4 subfamily C (AKR4C) is a group of aldo-keto reductases that are found in plants. Some AKR4C(s) in dicot plants are capable of metabolizing reactive aldehydes whereas, such activities have not been reported for AKR4C(s) from monocot species. In this study, we have screened Indica rice genome for genes with significant homology to dicot AKR4C(s) and identified a cluster of putative AKR4C(s) located on the Indica rice chromosome I. The genes including OsI_04426, OsI_04428 and OsI_04429 were successfully cloned and sequenced by qRT-PCR from leaves of Thai Jasmine rice (KDML105). OsI_04428, later named AKR4C14, was chosen for further studies because it shares highest homology to the dicot AKR4C(s). The bacterially expressed recombinant protein of AKR4C14 was successfully produced as a MBP fusion protein and his-tagged protein. The recombinant AKR4C14 were capable of metabolizing sugars and reactive aldehydes i.e. methylglyoxal, a toxic by-product of the glycolysis pathway, glutaraldehyde, and trans-2-hexenal, a natural reactive 2-alkenal. AKR4C14 was highly expressed in green tissues, i.e. leaf sheets and stems, whereas flowers and roots had a significantly lower level of expression. These findings indicated that monocot AKR4C(s) can metabolize reactive aldehydes like the dicot AKR4C(s) and possibly play a role in detoxification mechanism of reactive aldehydes.