Evaluation of the Resistance of Transgenic C5 Plum (Prunus domestica L.) against Four Chilean Plum Pox Virus Isolates through Micro-Grafting

Abstract

The transgenic plum (Prunus domestica L.) C5, in which the coat protein (CP) gene of the Plum pox virus (PPV) is inserted, represents a unique example of the use of genetic engineering for fruit crop improvement in Prunus spp. Field trials in Poland, Romania, and Spain have demonstrated resistance of C5 to several D and M strain PPV isolates. In Chile, the quarantine regulations for PPV and for genetically modified (GM) plants require that the testing of C5 for resistance to Chilean PPV isolates be done under controlled isolated conditions. To carry out these tests C5 shoots were multiplied in vitro and micro-grafted onto four Adesoto101 (Prunus insititia L.) rootstock populations that had been previously infected each with one of four Chilean PPV-Ds. Tests were carried out under controlled conditions in a biosafety greenhouse. Symptoms appearance, virus detection, and viral mRNA levels for the cylindrical inclusion (CI) and CP genes were determined during three consecutive growing seasons. Complete resistance to all PPV isolates was demonstrated during the first 2 yr in all of the C5 plants. In the third season, four of 10 C5 plants showed mild symptoms on leaves close to the graft union and low but detectable CI mRNA levels in the C5 scions. These results support the effectiveness of using of micro-grafting on P. insititia for PPV resistance studies, especially in the limited space of a quarantine facility; whereas resistance levels in C5 after 3 yr indicate the importance of long term and field scale evaluations.

Agrobacterium-Mediated Transformation of Russian Commercial Plum cv. “Startovaya” (Prunus domestica L.) With Virus-Derived Hairpin RNA Construct Confers Durable Resistance to PPV Infection in Mature Plants

“…Fortunately, C-5 has generated after the spontaneous rearrangement of PPV coat protein (CP) sequences into an inverted repeat/hairpin configuration during the Agrobacterium -mediated transformation. This resulted in activation of RNA silencing process in regenerated C-5 plant ( Kundu et al, 2008 ), and thus provided long time viral resistance confirmed later by various greenhouse tests and field trials ( Capote et al, 2008 ; Polák et al, 2008 , 2017 ; Wong et al, 2009 ; Scorza et al, 2013 ). Soon it was shown that the introduction of ihpRNA constructs, specifically engineered by joining of the viral fragment as inverted repeats separated by a spacer or an intron, significantly increase the silencing efficiency in host plants ( Khalid et al, 2017 ).…”