Abstract
BackgroundIn plants, host factors encoded by susceptibility (S) genes are indispensable for viral infection. Resistance is achieved through the impairment or the absence of those susceptibility factors. Many S genes have been cloned from model and crop species and a majority of them are coding for members of the eukaryotic translation initiation complex, mainly eIF4E, eIF4G and their isoforms. The aim of this study was to investigate the role of those translation initiation factors in susceptibility of stone fruit species to sharka, a viral disease due to Plum pox virus (PPV).ResultsFor this purpose, hairpin-inducing silencing constructs based on Prunus persica orthologs were used to generate Prunus salicina (Japanese plum) 4E and 4G silenced plants by Agrobacterium tumefaciens-mediated transformation and challenged with PPV. While down-regulated eIFiso4E transgenic Japanese plums were not regenerated in our conditions, eIFiso4G11-, but not the eIFiso4G10-, silenced plants displayed durable and stable resistance to PPV. We also investigated the alteration of the si- and mi-RNA profiles in transgenic and wild-type Japanese plums upon PPV infection and confirmed that the newly generated small interfering (si) RNAs, which are derived from the engineered inverted repeat construct, are the major contributor of resistance to sharka.ConclusionsOur results indicate that S gene function of the translation initiation complex isoform is conserved in Prunus species. We discuss the possibilities of using RNAi silencing or loss-of-function mutations of the different isoforms of proteins involved in this complex to breed for resistance to sharka in fruit trees.
Highlights
In plants, host factors encoded by susceptibility (S) genes are indispensable for viral infection
While those previous studies demonstrated that the eIFiso4F complex is essential for Plum pox virus (PPV) infection in Arabidopsis, genetic evidence obtained from other pathosystems indicated that potyviruses have a specific requirement for a given 4F or iso4F complex depending on the host plants
Generation of transgenic Japanese plum trees The RNAi constructs described in the Methods section were used to transform Japanese plum cultivars, Angeleno (AG) and Larry-Ann (LA), and seventy-three transgenic, NPTII-positive plants were obtained, of which seventeen were transferred to high confinement greenhouse at INRA (France) for PPV resistance testing (Additional file 7: Table S1)
Summary
Host factors encoded by susceptibility (S) genes are indispensable for viral infection. The aim of this study was to investigate the role of those translation initiation factors in susceptibility of stone fruit species to sharka, a viral disease due to Plum pox virus (PPV). The eIFiso4F complex, is composed of the eIFiso4E and eIFiso4G isoforms Because of their essential role in viral infection, the eIF4E and eIF4G translation initiation factors (and isoforms) are coded by host genes hereafter referred to as susceptibility (S) genes [6]. Nicaise et al [21] revealed that an Arabidopsis translationally non-functional eifiso4g1 mutant is resistant to PPV, but not its eifiso4g2 and eif4g knocked-out counterparts While those previous studies demonstrated that the eIFiso4F complex is essential for PPV infection in Arabidopsis, genetic evidence obtained from other pathosystems indicated that potyviruses have a specific requirement for a given 4F or iso4F complex depending on the host plants. This hypothesis could not be tested in the European plum eIFiso4E-silenced plants which have died (Tian L et al, personal communication)
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