| Title: | Investigating inducible short-chain alcohol dehydrogenases/reductases clarifies rice oryzalexin biosynthesis |
| Author(s): | Kitaoka N; Wu Y; Zi J; Peters RJ; |
| Address: | "Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, 50011, USA" |
| ISSN/ISBN: | 1365-313X (Electronic) 0960-7412 (Print) 0960-7412 (Linking) |
| Abstract: | "Rice (Oryza sativa) produces a variety of labdane-related diterpenoids as phytoalexins and allelochemicals. The production of these important natural products has been partially elucidated. However, the oxidases responsible for production of the keto groups found in many of these diterpenoids have largely remained unknown. Only one short-chain alcohol dehydrogenase/reductases (SDRs), which has been proposed to catalyze the last step in such a pathway, has been characterized to date. While rice contains >220 SDRs, only the transcription of five has been shown to be induced by the fungal cell wall elicitor chitin. This includes the momilactone A synthase (OsMAS/SDR110C-MS1), with the other four all falling in the same SDR110C family, further suggesting roles in diterpenoid biosynthesis. Here, biochemical characterization with simplified substrate analogs was first used to indicate potential functions, which were then supported by further analyses with key biosynthetic intermediates. Kinetic studies were then employed to further clarify these roles. Surprisingly, OsSDR110C-MS2 more efficiently catalyzes the final oxidation to produce momilactone A that was previously assigned to OsMAS/SDR110C-MS1, and we speculate that this latter SDR may have an alternative function instead. Conversely, two of these SDRs clearly appear to act in oryzalexin biosynthesis, with OsSDR110C-MI3 readily oxidizing the 3alpha-hydroxyl of oryzalexin D, while OsSDR110C-MS3 can also oxidize the accompanying 7beta-hydroxyl. Together, these SDRs then serve to produce oryzalexins A-C from oryzalexin D, essentially completing elucidation of the biosynthesis of this family of rice phytoalexins" |
| Keywords: | Alcohol Dehydrogenase/genetics/*metabolism Diterpenes/metabolism Oryza/*enzymology/genetics/*metabolism Pheromones/metabolism Plant Proteins/genetics/*metabolism Sesquiterpenes/metabolism Phytoalexins allelochemicals biosynthesis diterpenoids oxidases; |
| Notes: | "MedlineKitaoka, Naoki Wu, Yisheng Zi, Jiachen Peters, Reuben J eng R01 GM109773/GM/NIGMS NIH HHS/ Research Support, N.I.H., Extramural England 2016/06/24 Plant J. 2016 Oct; 88(2):271-279. doi: 10.1111/tpj.13249. Epub 2016 Sep 1" |
