Hamideh Raeisi - Department of Plant Protection, Faculty of Agricultural Sciences, Guilan University, Rasht, Iran.
Mohammad Reza Safarnejad - Department of Plant Viruses, Iranian Research Institute of Plant Protection, Agricultural Research Education and Extension Organization of Iran (AREEO), Tehran, Iran.
Seyed Mehdi Alavi - Department of Plant Biotechnology, National Institute of Genetic Engineering and Biotechnology, Tehran, Iran.
Naser Farrokhi - Department of Cell & Molecular Biology, Faculty of Life Sciences & Biotechnology, Shahid Beheshti University G. C, Tehran, Iran.
Seyed Ali Elahinia - Department of Plant Protection, Faculty of Agricultural Sciences, Guilan University, Rasht, Iran.
Hossein Safarpour - Cellular and Molecular Research Center, Birjand University of Medical Sciences, Birjand, Iran.
Farshid Sharifian - Department of Plant Biotechnology, National Institute of Genetic Engineering and Biotechnology, Tehran, Iran.

The Xanthomonas citri pv. citri (Xcc) is causal agent of bacterial citrus canker which is major disease of citrus throughout the world. The pthA bacterial effector protein is presented within the infected plants and indispensable of canker. The scFv antibodies are valuable tools for diagnosis and suppression of pathogens within plants. The present article describes developing and characterization of specific recombinant monoclonal scFv antibodies against pthA effector protein. For this aim, the gene encoding pthA protein was heterologously expressed in Escherichia coli and used for screening of Tomlinson phage display antibody library to pinpoint specific single chain variable fragment (scFv). In each round of panning, the affinity of phage towards pthA was checked by enzyme linked immunosorbent assay (ELISA). The data was indicative of about ۵۰% of the monoclonal phages to be reactive strongly against pthA protein. Among the positive clones, ۵ samples (A۱۲, B۸, C۱, H۸ and G۸) were capable of detecting Xcc-infected plant samples and recombinant pthA protein. Restriction fragment length polymorphism showed similar banding pattern for all ۵ scFvs as renamed to pthA-scFG۸. HB۲۱۵۱ E. coli cells were infected by the phage bearing pthA-scFG۸, and the expression of the peptide was induced by IPTG to produce a ۳۰ kDa recombinant molecule. I-TASSER was used for homology modeling of both scFv and pthA and docking was carried out by Hex program. The latter demonstrated binding energy of −۷۸۴ kcal/mol in scFv-pthA.

Biopanning, citrus bacterial canker, phage display, single chain fragment variable