Investigating the role of transgenic rootstock-mediated protection of non-transgenic scion

Investigating the role of transgenic rootstock-mediated protection of non-transgenic scion

Report Date: 12/01/2021
Project: 18-007   Year: 2021
Category: Plant Improvement
Author: Manjul Dutt
Sponsor: Citrus Research and Development Foundation

The objectives of this project are: 1.         Evaluate existing transgenic Carrizo and Swingle AtNPR1 overexpressing rootstocks in the laboratory and greenhouse. 2.         Conduct a replicated field trial with the best transgenic rootstocks budded with non-transgenic `Valencia’ and test for GMO gene products in the fruit or juice. 3.         Produce additional transgenic rootstock lines and stack other gene(s) responsible for SAR using mature transformation.  4.         Evaluate transgene segregation analyses of the rootstock progeny and large-scale propagation of select lines Obj 1: Transgenic rootstocks (n=12) that were budded with non-transgenic scion were side grafted with HLB infected budwood and maintained in the greenhouse. 6 months following infection trees were tested for the presence of HLB and were also evaluated for PR1 gene expression. PR1 is a SAR marker. We observed that all scions (with transgenic rootstock or non-transgenic control) were infected within a year of inoculation. There was no statistical difference between the treatments and control for the first 18 months. In several transgenic rootstock lines, Ct values did not decline at the same rate as controls after 18 months of infection. In several transgenic rootstock  – non transgenic scion combinations, there was also an enhanced expression of the PR1 gene, which indicated an active defense mechanism. At the termination of the project, all lines with enhanced PR1 gene expression were alive, albeit infected.  4 of the 12 controls died while 6 more exhibited enhanced HLB symptoms. Only one control could be considered an outlier with mild HLB symptoms at the termination of the project. Obj 2: This objective was in progress at the termination of the project with rootstock lines clonally propagated in the mist bed and ready to be budded with non-transgenic scion. Obj 3: 61 transgenic lines (Carrizo, US942) with different genes stacked with NPR1 were produced by the mature transformation lab. Most of these tested were determined to produce adequate transprotein. At the termination of the project, all lines were being sized up in the greenhouse for clonal propagation. Additionally, several select lines were budded onto standard trifoliate rootstocks for field planting. This was being planned for seed production. Obj 4: This objective  – field based under USDA BRS permit could not be initiated due to termination of the project  


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