R/Avr gene expression study of Rpi-vnt1.1 transgenic potato resistant to the Phytophthora infestans clonal lineage EC-1

Abstract

the Rpi-vnt1.1 gene was shown to be rapidly increased by two-fold and subsequently to have steady state expression for at least 5 days after the inoculation. The Rpi-vnt1.1 gene in addition to other R genes as a stack in farmers' preferred varieties will confer extreme resistance to late blight disease and rotations of plants with different R-gene-stack in time is likely to last longer than plants with single R gene.

Stacking three late blight resistance genes from wild species directly into African highland potato varieties confers complete field resistance to local blight races

“…Transformation efficiency of ‘Desiree’ (3.4%) was not affected by the relatively large size of the T‐DNA (18 585 bp). Indeed, transformation efficiency of ‘Desiree’ with single R gene construct was previously reported as 3.7% for RB gene, 6% for Rpi‐blb2 gene and 7.5% for Rpi‐vnt1.1 gene (Orbegozo et al ., ; Román et al ., , ). The variety ‘Victoria’ had lower transformation efficiency (1.5%) and took longer to produce regenerants.…”

“…This observation comes from the whole‐plant bioassay using the POX067 isolate which is able to infect the ‘Desiree’ and ‘Victoria’ varieties; it was used previously to select transgenic events with one of the three R genes, and has been used for selecting the transgenic events with the 3 R ‐gene stack. Indeed, the frequency of extreme resistant transgenic events is rather low when using single R genes, as we have reported previously: two out of 64 transgenic events with the RB gene alone, three out of 97 with the Rpi‐blb2 gene, and five out of 52 with the Rpi‐vnt1.1 gene (Orbegozo et al ., ; Román et al ., , ). However, out of 97 transgenic events we observed 75 with extreme resistance with the 3 R ‐gene stack from the variety ‘Desiree’ (Figure ).…”

“…Early on, R gene expression was shown to be induced one or 2 days after inoculation with P. infestans, slowly decreasing over the next 3 days (Kramer et al ., ; Orbegozo et al ., ; Román et al ., ; Vleeshouwers et al ., ). We observed R gene expression in the 3 R ‐gene stack transgenic event, but at such a low level that statistically significant differences could not be observed.…”

“…Agrobacterium-mediated transformation, the identification of transgenic events by molecular techniques, and their LB resistance assessment were achieved using protocols which have been described in the single gene transformation studies reported previously (Orbegozo et al, 2016;Rom an et al, 2017). The PCR molecular characterization of the 3R-gene stack considered sequences with no homologs in the potato genome: (1) the overlapping regions between two consecutive R genes;…”

“…Avrvnt1 was discovered more recently though virulent strains from Poland and the Andean region (Foster et al ., ; Pais et al ., ). In this case, the Avrvnt1 effector gene is silenced in virulent isolates, which has been recently shown not to be permanent (Román et al ., ; Stefańczyk et al ., ). In an artificial adaptation experiment, neither RB nor Rpi‐blb2 genes selected virulent variants from a single isolate used to inoculate repeatedly or at high doses (Halterman and Middleton, ; Orbegozo et al ., ).…”