Generation of Sweet Orange Transgenic Lines and Evaluation of Citrus psorosis virus‐derived Resistance against Psorosis A and Psorosis B

Abstract

Citrus psorosis is a widespread serious disease of citrus caused by Citrus psorosis virus (CPsV). In Argentina and Uruguay, this disease is spread by an unknown vector and there is no natural resistance or tolerance to the disease. There are two types of psorosis, described according to the symptoms observed in citrus trees, psorosis A (PsA) and psorosis B (PsB). PsA protects against the severe effects of the more aggressive type PsB. We have applied pathogen‐derived resistance to create a defence mechanism against this virus disease. Sweet orange transgenic lines were obtained containing three different genes of CPsV (54k, 48k and 24k genes) taken from a PsA isolate (CPV‐4). Fourteen lines were selected containing 1, 2 or 3 copies of the transgenes and evaluated for their acquired resistance against PsA (CPV 4 from USA) and PsB (CPsV 189‐34 from Argentina) isolates. These lines were susceptible to both isolates when graft‐infected, although one of the lines carrying the cp gene (CP‐96 line) containing two copies of the transgene and expressing a low level of the coat protein showed a delay in symptom expression when inoculated with the PsB isolate.

Transformação genética de laranja doce (Citrus sinensis L. Osbeck) com o gene D4E1 dirigido pelos promotores CaMV35S ou AtPP2

“…Neste trabalho, cada planta transgênica apresentou diferentes padrões de integração e diferentes números de inserções do transgene no genoma, variando de uma a três cópias. Este valor está dentro do observado por outros autores em plantas de citros transgênicas de uma a quatro inserções (DUTT et al, 2012;REYES et al, 2011;ZANEK et al, 2008). Futuramente, estas plantas serão multiplicadas e avaliadas quanto à resistência ao cancro cítrico e ao HLB.…”

Transgenic Resistance

“…By contrast, transgenic sweet orange plants expressing hpRNAs from the 54-kDa gene on RNA2 showed little-to-no resistance and variable effects on virus accumulation (Reyes et al, 2009), as did transgenic sweet orange expressing hpRNAs of the p24 gene on RNA1 (Reyes, Zanek, et al, 2011). By contrast, transgenic sweet orange plants expressing hpRNAs from the 54-kDa gene on RNA2 showed little-to-no resistance and variable effects on virus accumulation (Reyes et al, 2009), as did transgenic sweet orange expressing hpRNAs of the p24 gene on RNA1 (Reyes, Zanek, et al, 2011).…”

Recent advances in Citrus psorosis virus

“…These plants were evaluated for their acquired resistance against two isolates, PsA (CPV-4) and PsB (CPsV 189-34), which differ in symptoms severity. These lines were susceptible to both isolates when graftinfected, although one of the lines carrying the CPG (CP-96 line) containing two copies of the transgene and expressing a low level of the CP showed a delay in symptom expression when inoculated with the PsB isolate [50]. These studies represent a first step to a possible control of CPsV, but the implementation of the technique requires time consuming in transformation procedure and multiplication.…”

“…Several citrus species have been transformed with the CPG of a severe strain of CPsV but presently there is little published information on the resistance of such plants to CPsV infection [23,48,49,50,81]. The same strategy was used by Zanek et al [81] producing 21 independent lines of transgenic sweet orange (CP-lines) expressing low and variable amounts of CPsV CP (isolate CPV-4).…”