Abstract
A previously unknown disease which causes severe vein thickening and inward leaf curl was observed in a number of opium poppy (Papaver somniferum L.) plants. The sequence analysis of full-length viral genome and associated betasatellite reveals the occurrence of Ageratum enation virus (AEV) and Ageratum leaf curl betasatellite (ALCB), respectively. Co-infiltration of cloned agroinfectious DNAs of AEV and ALCB induces the leaf curl and vein thickening symptoms as were observed naturally. Infectivity assay confirmed this complex as the cause of disease and also satisfied the Koch’s postulates. Comprehensive microscopic analysis of infiltrated plants reveals severe structural anomalies in leaf and stem tissues represented by unorganized cell architecture and vascular bundles. Moreover, the characteristic blebs and membranous vesicles formed due to the virus-induced disintegration of the plasma membrane and intracellular organelles were also present. An accelerated nuclear DNA fragmentation was observed by Comet assay and confirmed by TUNEL and Hoechst dye staining assays suggesting virus-induced programmed cell death. Virus-infection altered the biosynthesis of several important metabolites. The biosynthesis potential of morphine, thebaine, codeine, and papaverine alkaloids reduced significantly in infected plants except for noscapine whose biosynthesis was comparatively enhanced. The expression analysis of corresponding alkaloid pathway genes by real time-PCR corroborated well with the results of HPLC analysis for alkaloid perturbations. The changes in the metabolite and alkaloid contents affect the commercial value of the poppy plants.
Highlights
Geminiviruses of the family Geminiviridae infect a large range of crop and non-crop plants, and are considered as a major threat to the agriculture system globally, but consequences are more severe in warmer parts of the world
Ageratum enation virus (AEV) is emerging as a devastating pathogen in India and reported to cause significant losses in many crops (Kumar et al, 2013; Srivastava et al, 2013; Swarnalatha et al, 2013)
The present study identified the association of AEV and Ageratum leaf curl betasatellite (ALCB) with severe leaf curl and vein thickening disease of opium poppy for the first time
Summary
Geminiviruses of the family Geminiviridae infect a large range of crop and non-crop plants, and are considered as a major threat to the agriculture system globally, but consequences are more severe in warmer parts of the world. With the identification of novel viruses, the family Geminiviridae is extended into nine genera namely Mastrevirus, Curtovirus, Topocuvirus, Becurtovirus, Eragrovirus, Capulavirus, Grablovirus, Begomovirus, and Turncurtovirus, depending on the host range, insect-vector and genome characteristics (Zerbini et al, 2017). Begomoviruses have singlestranded circular DNA genome of about 2.8 kb coding for 5–7 viral proteins (Hanley-Bowdoin et al, 2013). These proteins collectively take over the host cellular processes, interfere with and suppress the plant defense system causing infection, and as a consequence the plants develop symptoms like leaf curling, leaf yellowing, leaf enation, leaf crumpling, vein thickening, and plant stunting. Fiber, and weed plants (Castillo-Urquiza et al, 2008), they have been reported to infect the medicinal and aromatic plants and affect produce quality (Saeed and Samad, 2016)
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