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Abstracts - Jéssica C. Amaral

BIOSYNTHETIC STUDY OF PYRANOCOUMARINS IN CITRUS AS A STRATEGY TO COMBAT CVC AND HLB

Jéssica C. Amaral¹*, Michelli M. da Silva¹, Mª. Fátima das Graças F. da Silva¹, Thayana da C. Alves¹, Antônio G. Ferreira¹, Edieidia S. Pina², Adriana A. Lopes², Ana Maria S. Pereira².

1 University Federal of São Carlos, Chemistry Department, Rodovia Washington Luís, 310, São Carlos - SP, Brazil. 2 University of Ribeirão Preto, Biotechnology Department, Av. Costábile Romano, 2201 - Ribeirânia, Ribeirão Preto – SP.

* jessica.camaral@yahoo.com.br

Coumarins are important compounds for the adaptation of plants to biotic or abiotic stresses and act as plant protectors against phytopathogens and insects¹. Within this class, pyranocoumarins are a sub-group of more than 1500 natural coumarins, essentially found in four families of superior plants: Apiaceae, Fabaceae, Moraceae, Rutaceae and are distributed through all species of Citrus. Coumarins, like other phenylpropanoids, have biosynthetic origin in p-coumaric acid and their great structural diversity is mainly due to the incorporation of prenyl units in the benzene ring. In order to get a response about the prenylation reaction, isotopic labeling experiments were performed to confirm the biosynthesis of xanthyletin and seselin.

To verify if the prenylation reaction of umbelliferone in C6 and C8, which leads to the precursors demethylsuberosin and osthenol occurs via MEV or via MEP, terpenic biosynthesis portion of xanthyletin and seselin was investigated by incorporation of glucose-1- [¹³C] in C. sinensis and C. limonia roots. The isotopic labeling studies are of great importance, since they allow the determination of the operating pathway. Depending on the metabolism route involved, the carbon marking of the isoprene units will be differentiated. Therefore, for the confirmation of the biosynthetic route, quantitative NMR experiments were carried out to determine which carbons of the terpene unit are enriched. If the labeling is observed at the C-2, C-4 and C-5 carbons, biosynthesis occurs via MEV and if observed at C-1 and C-5 occurs via MEP². Both pathways may also occur concomitantly with all enriched carbons except C-3. The enrichment pattern was then determined from the comparison of the ¹³C NMR spectra of both pyranocoumarins isolated from roots of C. sinensis and C. limonia cultured in MS basal medium - 100% glucose and in MS basal medium - 75% glucose -1- [¹³C]. The results showed that the isoprene moiety derives exclusively from MEP pathway, because only the C-1 and C-5 carbons of the IPP unit, for both xanthyletin C-1 (δ 120.3 ppm) and C-5 (δ 27.15) and for seselin C-1 (δ 115.67) and C-5 (δ 28.54) were enriched.

  1. Vialart G, et al. A 2-oxoglutarate-dependent dioxygenase from Ruta graveolens L. exhibits p-coumaroyl coA 2’-hydroxylase activity (C2’H): a missing step in the synthesis of umbelliferone in plants. Plant J. 2012, v. 70, p. 460-470.

  2. Lopes, A. A. et al. A biosynthetic pathway of sesquiterpene lactones in Smallanthus sonchifolius and their localization in leaf tissues by MALDI imaging. Chem. Com. 2013, v. 49, p. 9989-9991.