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

Sakuranetin ( 1 ) is a rice flavanone-type phytoalexin. We have already reported that the metabolites from the detoxification of 1 by Pyricularia oryzae are naringenin ( 2 ) and sternbin. In this study, we investigated whether the rice sheath blight fungus Rhizoctonia solani , 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 -β-d-xylopyranoside ( 3 ), and naringenin-7- O -β-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.