Detection and partial characterization of a putative closterovirus affecting Ficus carica: molecular, ultrastructural and physiological aspects of infected leaves

Abstract

Fig mosaic disease (FMD) was systemically transmitted to susceptible fig plants by grafting and led to development of symptoms including a wide array of discoloration, green blisters, mottling, crinkling and deformation of leaves and fruits. A sensitive assay for the detection of FMV using specific enzyme-linked immune sorbent assay and reverse transcription-polymerase chain reaction was developed. A double-stranded RNA ca. 19 kbp in size was obtained from the fig tissue extract and used as a template. A cDNA fragment (350 bp) of phosphate motifs 1 and 2 of the heat shock-protein 70 homologue of the family Closteroviridae was amplified using a specific primer set. Virions were flexuous filaments up to 1,800 nm in length and ~21 nm in diameter. Viral infection formed new polypeptides in leaves that reflect pathogen-related proteins. Total photosynthetic pigment contents of virus-infected leaves decreased by 33.06%, with a raise in chl a/b ratio that was mainly caused by a decline in chl b content. Chloroplasts of virus-infected leaves lost their envelopes, and the internal structures of grana and stroma thylakoids were deformed and turned to spherical shapes. No virus inclusion bodies were detected in chloroplasts or other mesophyll cell organelles. Starch grains of chloroplasts were absent in the virus-infected leaves. Viral infection caused a decline in catalase and induction in peroxidase activities in leaves. Levels of thiobarbituric acid reactants in viral-infected leaves increased by 15%, while the content of total phenolics increased by 29%, in respect to healthy ones. The present results indicate a possible presence of Fig leaf mottle-associated virus-1 (FLMaV-1) in fig trees and provide an overview of the negative effects on fig leaves in response to FLMaV-1 infection from morphological, physiological and subcellular perspectives.