Viral-Like Symptoms Induced by the Ectopic Expression of the p23 Gene of Citrus tristeza virus Are Citrus Specific and Do Not Correlate with the Pathogenicity of the Virus Strain

Abstract

Ectopic expression of the p23 gene from a severe (T36) strain of Citrus tristeza virus (CTV) induces viral-like symptoms in Mexican lime. Here, we report that expressing the same gene from a mild strain induced similar symptoms that correlated with accumulation of p23 protein irrespective of the source strain. CTV inoculation of transgenic limes showing CTV-like leaf symptoms and high p23 accumulation did not modify symptoms initially, with the virus titer being as in inoculated nontransgenic controls; however, at later stages, symptoms became attenuated. Transformation with p23-T36 of CTV-susceptible sweet and sour orange and CTV-resistant trifoliate orange also led to CTV-like leaf symptoms that did not develop when plants were transformed with a truncated p23 version. In transgenic citrus species and relatives other than Mexican lime, p23 was barely detectable, although symptom intensity correlated with levels of p23 transcripts. The lower accumulation of p23 in sweet and sour orange compared with Mexican lime also was observed in nontransgenic plants inoculated with CTV, suggesting that minimal p23 levels cause deleterious effects in the first two species. Conversely, transgenic expression of p23 in CTV nonhost Nicotiana spp. led to accumulation of p23 without phenotypic aberrations, indicating that p23 interferes with plant development only in citrus species and relatives.

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).…”

Molecular Virology and Pathogenicity of Citrus tristeza virus

“…However, these transgene-induced symptoms differ substantially from the virus-induced SY of uniform chlorosis and stunting of new shoot growth in sour orange ( Figure 5). Transgenic limes differ from virus-infected limes in that symptom severity is proportional to the levels of p23 production, not to the source or sequence of the gene (Fagoaga et al, 2005;Ghorbel et al, 2001), whereas the symptom intensity in virus-infected limes is dramatically different between severe and mild isolates of virus. Yet, the different response in transgenic plants could be related to the fact that the p23 protein is produced constitutively in most cells, while in nature the expression of p23 ORF from the viral genome is limited to phloem-associated cells (Albiach-Marti et al, 2010).…”

“…However, transgenic Mexican lime plants develop more intense vein clearing in the plant leaves and symptomatology like chlorotic pinpoints in leaves, stem necrosis and collapse (Ghorbel et al, 2001) that differs from those induced by natural virus infection ( Figure 5). Additionally, transgenic sour orange plants expressing p23 develop vein clearing, leaf deformation, defoliation, and shoot necrosis (Fagoaga et al, 2005). However, these transgene-induced symptoms differ substantially from the virus-induced SY of uniform chlorosis and stunting of new shoot growth in sour orange ( Figure 5).…”

“…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.…”

Molecular characterization of Citrus tristeza virus strains in Peninsular Malaysia

“…Tel: 0060192210540. Fax: 0060356860698. 2007) and are composed of a positive sense, single stranded genomic RNA about 20 kb in size (Che, et al, 2002;Hilf, et al, 1995;Huang, et al, 2004;Ruiz-Ruiz, et al, 2007) that contains 12 open reading frame (ORFs) (Che et al, 2002;Fagoaga et al, 2005;Narvaez et al, 2000;Satyanarayana et al, 2001) and encode at least 19 proteins (Che et al, 2002;Che et al, 2001;Huang et al, 2004;Satyanarayana et al, 2001). Two of these proteins are capsid proteins of 25 and 27 kDa which comprise about 95 and 5% of the virus coat, respectively (BarJoseph et al, 1989;Jiang, et al, 2008;Roy, et al, 2005;Ruiz-Ruiz et al, 2007).…”