Discovery of inhibitors of the ferredoxin-NADP+ reductase from the Xanthomonas citri subsp. citri phytopathogen

MARTÍNEZ-JÚLVEZ M; TONDO ML; MEDINA M; IONESCU I; ORELLANO EG; GOÑI G; PETROCELLI S

Sevilla

Congreso; 16th Congress of the Spanish Biophysical Society; 2017

Spanish Biophysical Society

Plant type Ferredoxin-NADP(H) reductases (FNRs, EC 1.18.1.2) constitute a family of FAD containing enzymes that deliver NADPH or low potential one-electron donors to redox-based metabolisms in plastids and bacteria. Based on phylogenetic analysis, FNRs present in most prokaryotes (collectively known as FPRs) have been classified into two subclasses represented by the Azotobacter vinelandii (subclass I) and the Escherichia coli (subclass II) [1]. Xanthomonas axonopodis citri subsp. citri (Xcc) is a Gram-negative bacterium responsible for citrus canker, a disease that affects most commercial citrus crops and has economic impact worldwide [2]. Its fpr gene encodes a subclass I FPR (XccFPR). The role of XccFPR nor its potential substrate have been elucidated, but its involvement in the oxidative stress response of X. citri via interaction with ferredoxin XAC1762 has been proposed [3]. Therefore, Xcc FPR is relevant for the pathogen survival and the inhibition of its activity might represent an effective treatment against citrus canker. We started performing a highthroughput screening (HTS) of a library of 11120 druglike compounds to find inhibitors of XccFPR based on its diaphorase activity. We selected 43 HTS hits and narrowed them down to 5 primary hits that showed IC 50 values in the low micromolar range and successfully abolished the activity of XccFPR. The four best inhibitors were assayed in vivo on plate cultures, and two of them showed bacterial growth inhibition. Based on the best primary hit, secondary hits were selected and one of them improved the characteristics of the primary one. Type of inhibition of this hit was determined and its effect on plastidic type FNR. This work is in progress but represents a promising pathway for the development of phytosanitary compounds against citrus canker propagation.[1] E. A. Ceccarelli et al. BBA, 1698, 155-165, 2004.[2] J. H. Graham et al. Mol Plant Pathol, 5, 1-15, 2004.[3] M. L Tondo et al. PLoS One, 6, e27124, 2011.