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Planta

Title:		"Identification and characterization of cytochrome P450 CYP77A59 of loquat (Rhaphiolepis bibas) responsible for biosynthesis of phenylacetonitrile, a floral nitrile compound"
Author(s):		Yamaguchi T; Nomura T; Asano Y;
Address:		"Biotechnology Research Center, Department of Biotechnology, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama, 939-0398, Japan. t-yamaguchi@pu-toyama.ac.jp. Biotechnology Research Center, Department of Biotechnology, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama, 939-0398, Japan"
Journal Title:		Planta
Year:		2023
Volume:		20230511
Issue:		6
Page Number:		114 -
DOI:		10.1007/s00425-023-04151-x
ISSN/ISBN:		1432-2048 (Electronic) 0032-0935 (Linking)
Abstract:		"Cytochrome P450 CYP77A59 is responsible for the biosynthesis of phenylacetonitrile in loquat flowers. Flowers of some plants emit volatile nitrile compounds, but the biosynthesis of these compounds is unclear. Loquat (Rhaphiolepis bibas) flowers emit characteristic N-containing volatiles, such as phenylacetonitrile (PAN), (E/Z)-phenylacetaldoxime (PAOx), and (2-nitroethyl)benzene (NEB). These volatiles likely play a defense role against pathogens and insects. PAN and NEB are commonly biosynthesized from L-phenylalanine via (E/Z)-PAOx. Two cytochrome P450s-CYP79D80 and 'promiscuous fatty acid omega-hydroxylase' CYP94A90, which catalyze the formation of (E/Z)-PAOx from L-phenylalanine and NEB from (E/Z)-PAOx, respectively-are involved in NEB biosynthesis. However, the enzymes catalyzing the formation of PAN from (E/Z)-PAOx in loquat have not been identified. In this study, we aimed to identify candidate cytochrome P450s catalyzing PAN formation in loquat flowers. Yeast whole-cell biocatalyst assays showed that among nine candidate cytochrome P450s, CYP77A58 and CYP77A59 produced PAN from (E/Z)-PAOx. CYP77As catalyzed the dehydration of aldoximes, which is atypical of cytochrome P450; the reaction was NADPH-dependent, with an optimum temperature and pH of 40 degrees C and 8.0, respectively. CYP77As acted on (E/Z)-PAOx, (E/Z)-4-hydroxyphenylacetaldoxime, and (E/Z)-indole-3-acetaldoxime. Previously characterized CYP77As are known to hydroxylate fatty acids; loquat CYP77As did not act on tested fatty acids. We observed higher expression of CYP77A59 in flowers than in buds; expression of CYP77A58 was remarkably reduced in the flowers. Because the flowers, but not buds, emit PAN, CYP77A59 is likely responsible for the biosynthesis of PAN in loquat flowers. This study will help us understand the biosynthesis of floral nitrile compounds"
Keywords:		*Nitriles/analysis/metabolism *Eriobotrya Cytochrome P-450 Enzyme System/genetics Flowers/metabolism Phenylalanine Fatty Acids/analysis Cyp77a Cytochrome P450 Flower scent Loquat Phenylacetonitrile Plant specialized metabolism;
Notes:		"MedlineYamaguchi, Takuya Nomura, Takuya Asano, Yasuhisa eng 18K14385/Japan Society for the Promotion of Science/ 20K05861/Japan Society for the Promotion of Science/ Germany 2023/05/11 Planta. 2023 May 11; 257(6):114. doi: 10.1007/s00425-023-04151-x"