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Xylosylated Detoxification of the Rice Flavonoid Phytoalexin Sakuranetin by the Rice Sheath Blight Fungus Rhizoctonia solani.

ABSTRACT: Sakuranetin (1) is a rice flavanone-type phytoalexin. We have already reported that the metabolites from the detoxification of 1 by Pyriculariaoryzae are naringenin (2) and sternbin. In this study, we investigated whether the rice sheath blight fungus Rhizoctoniasolani, another major rice pathogen, can detoxify 1. The extract of R. solani suspension culture containing 1 was analyzed by LC-MS to identify the metabolites of 1. Three putative metabolites of 1 were detected in the extract from the R. solani suspension culture 12 h after the addition of 1, and they were identified as 2, sakuranetin-4'-O-?-d-xylopyranoside (3), and naringenin-7-O-?-d-xylopyranoside (4) by NMR, LC-MS/MS, and GC-MS analyses. The accumulation of 2, 3, and 4 reached their maximum levels 9-12 h after the addition of 1, whereas the content of 1 decreased to almost zero within 9 h. The antifungal activities of 3 and 4 against R. solani were negligible, and 2 showed weaker antifungal activity than 1. We concluded that 2, 3, and 4 are metabolites from the detoxification of 1 by R. solani. Xylosylation is a rare and efficient detoxification method for phytoalexins.

SUBMITTER: Katsumata S

PROVIDER: S-EPMC6017487 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Xylosylated Detoxification of the Rice Flavonoid Phytoalexin Sakuranetin by the Rice Sheath Blight Fungus Rhizoctonia solani.

Katsumata Shun S Toshima Hiroaki H Hasegawa Morifumi M

Molecules (Basel, Switzerland) 20180129 2

Sakuranetin (1) is a rice flavanone-type phytoalexin. We have already reported that the metabolites from the detoxification of 1 by Pyriculariaoryzae are naringenin (2) and sternbin. In this study, we investigated whether the rice sheath blight fungus Rhizoctoniasolani, another major rice pathogen, can detoxify 1. The extract of R. solani suspension culture containing 1 was analyzed by LC-MS to identify the metabolites ...[more]

PMID: 29382171

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Project description:Sakuranetin, the major flavonoid phytoalexin in rice, can be induced by ultraviolet (UV) irradiation, treatment with CuCl 2 or jasmonic acid (JA), or phytopathogenic infection. In addition to sakuranetin's biological significance on disease resistance in rice, its broad bioactivities have recently been described. Results from these studies have shown that sakuranetin is a useful compound as a plant antibiotic and a potential pharmaceutical agent. Sakuranetin is biosynthesized from naringenin, a precursor of sakuranetin, by naringenin 7-O-methyltransferase (NOMT), but the relevant gene has not yet been identified in rice. Recently, we identified the OsNOMT gene, which is involved in the final step of sakuranetin biosynthesis in rice. In previous studies, OsNOMT was purified to apparent homogeneity from UV-treated wild-type rice leaves; however, the purified protein, termed OsCOMT1, exhibited caffeic acid 3-O-methyltransferase (COMT) activity, but not NOMT activity. Based on the analysis of an oscomt1 T-DNA tagged mutant, we determined that OsCOMT1 did not contribute to sakuranetin production in rice in vivo. Therefore, we took advantage of the oscomt1 mutant to purify OsNOMT. A crude protein preparation from UV-treated oscomt1 leaves was subjected to three sequential purification steps resulting in a 400-fold purification from the crude enzyme preparation with a minor band at an apparent molecular mass of 40 kDa in the purest enzyme preparation. Matrix-assisted laser desorption/ionization time of flight/time of flight analysis showed that the 40 kDa protein band included two O-methyltransferase-like proteins, but one of the proteins encoded by Os12g0240900 exhibited clear NOMT activity; thus, this gene was designated OsNOMT. Gene expression was induced by treatment with jasmonic acid in rice leaves prior to sakuranetin accumulation, and the recombinant protein showed reasonable kinetic properties to NOMT. Identification of the OsNOMT gene enables the production of large amounts of sakuranetin through transgenic rice and microorganisms. This finding also allows for the generation of disease-resistant and sakuranetin biofortified rice in the future.

Dataset Information

Xylosylated Detoxification of the Rice Flavonoid Phytoalexin Sakuranetin by the Rice Sheath Blight Fungus Rhizoctonia solani.

Publications

Xylosylated Detoxification of the Rice Flavonoid Phytoalexin Sakuranetin by the Rice Sheath Blight Fungus Rhizoctonia solani.

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