Transgenic citrus plants expressing the citrus tristeza virus p23 protein exhibit viral‐like symptoms

Abstract

Summary The 23 kDa protein (p23) coded by the 3′‐terminal gene of Citrus tristeza virus (CTV), a member of the genus Closterovirus with the largest genome among plant RNA viruses, is an RNA‐binding protein that contains a motif rich in cysteine and histidine residues in the core of a putative zinc‐finger domain. On this basis, a regulatory role for CTV replication or gene expression has been suggested for p23. To explore whether over‐expression of this protein in transgenic plants could affect the normal CTV infection process, transgenic Mexican lime plants were generated carrying the p23 transgene, or a truncated version thereof, under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Constitutive expression of p23 induced phenotypic aberrations that resembled symptoms incited by CTV in non‐transgenic lime plants, whereas transgenic plants expressing the p23 truncated version were normal. The onset of CTV‐like symptoms in p23‐transgenic plants was associated with the expression of p23, and its accumulation level paralleled the intensity of the symptoms. This demonstrates that p23 is involved in symptom development and that it most likely plays a key role in CTV pathogenesis. This is the first case in which a protein encoded by a woody plant‐infecting RNA virus has been identified as being directly involved in pathogenesis in its natural host. This finding also delimits a small region of the large CTV genome for the future mapping of specific pathogenic determinants.

Citrus tristeza virus infection induces the accumulation of viral small RNAs (21–24-nt) mapping preferentially at the 3′-terminal region of the genomic RNA and affects the host small RNA profile

“…Besid es, p23, an RN A-bind ing protein (López et al 2000) that controls the asym m etrical accum ulation of (+) and (-) CTV RN As (Satyanarayana et al 2002), is a pathogenicity d eterm inant w hen expressed ectopically in several Citrus spp. (Fagoaga et al 2005;Ghorbel et al 2001) and a likely d eterminant of the seed ling yellow s synd rom e incited by CTV in sour orange (Citrus aurantium L.) and grapefruit (C. paradisi Macf.) (Albiach-Martí et al 2010).…”

Recent Advances in Fruit Species Transformation

“…Contrary to conventional plant breeding, this technology can integrate foreign DNA into different plant cells to produce transgenic plants with new desirable traits (Chilton et al, 1977;Newell, 2000). These biotechnological approaches are a great option to improve fruit genotypes with significant commercial properties such as increased biotic (resistance to disease of virus, fungi, pests and bacteria) (Ghorbel et al, 2001;Fagoaga et al, 2001;Fagoaga et al, 2006;Fagoaga et al, 2007) or abiotic (temperature, salinity, light, drought) stress tolerances (Fu et al, 2011); nutrition; yield and quality (delayed fruit ripening and longer shelf life) and to use as bioreactor to produce proteins, edible vaccines and biodegradable plastics (Khandelwal et al, 2011).…”

Molecular Virology and Pathogenicity of Citrus tristeza virus

“…However, hybrid constructs, which carried exchanges of T30 CP and CPm into the T36 genome, failed to passage through successive sets of N. benthamiana protoplasts (Albiach-Marti et al, 2010), probably due to deficient heteroencapsidation since incomplete virions do not withstand this procedure (Satyanarayana et al, 2000;. Other methodology used to map disease determinants was the expression of CTV proteins in transgenic plants (Fagoaga et al, 2005;Ghorbel et al, 2001). When p23 is ectopically expressed in transgenic citrus induces virus-like symptoms.…”