Testing grapefruit trees expressing an anti-NodT antibody for resistance to HLB

Testing grapefruit trees expressing an anti-NodT antibody for resistance to HLB

Report Date: 03/30/2021
Project: 18-016   Year: 2021
Category: Plant Improvement
Author: Tim McNellis
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: This report covers the period of December 1, 2020 – February 28, 2021.  The objective of this project is to test transgenic ‘Ducan’ grapefruit trees expressing an anti-HLB antibody fused to the FT (Flowering Locus T) protein (FT-scFv protein).  Several accomplishments were made during this reporting period.  Graduate student Mr. Chad Vosburg was able to take a trip to Florida to assess trees, take samples, and send samples for qPCR analysis at Southern Gardens.  Chad visited Fort  Pierce for more than one month from late December, 2020, to late January, 2021.   He took samples from a field trial natural inoculation, an Asian citrus psyllid (ACP) infection in the greenhouse, and a graft challenge with FT-scFv scions grafted to HLB-infected rough lemon rootstocks. These samples were prepared and sent to Southern Gardens for qPCR detection and quantification of ‘Candidatus Liberibacter asiaticus’ (CLas) within the tissues.  Data are anticipated to be received from these samples in March, 2021.  In addition, growth data were taken from FT-scFv  scions on infected rough lemon.  The transgenic scions appeared to be consistently growing faster and more robustly than the control non-transgenic scions.  However, these data are still being analyzed and we anticipate full analysis in the next reporting period.  A second run of this experiment was initiated by additional grafting of transgenic and control scions to infected and uninfected rough lemon during Chad’s most recent visit in order to determine whether this effect is replicable.    Finally, our publication of the accelerated blooming phenotype of FT-scFv transgenics was published in the February issue of Plant Biotechnology Journal and was honored with being selected as the cover feature of that issue.  A copy of  the finalized publication and journal cover is included in this report.  2. Please state what work is anticipated for next quarter:qPCR data from the field, graft, and psyllid-transmission HLB challenge tests will be received from Southern Gardens in March, 2021.  These data will be analyzed during the next reporting period.  Additional sampling of plants from the psyllid-inoculated and field grown trees will be performed with help from collaborators at University of Florida and the USDA USHRL.  These will be sent to Southern Gardens for qPCR CLas quantification for an additional infection time point.  In March, 2021, we plan to submit a request for a second, six-month, no-cost extension in order to complete the time courses for CLas quanitification and characterization of any potential HLB tolerance of the FT-scFv transgenic lines.  This no cost extension request will be especially critical to completing the field test of the transgenics, since so far we do not detect CLas infections in those trees.   In addition, it will be important to re-test the graft-transmission response of the FT-scFv scions to CLas infection, since it appears that they may have some tolerance to CLas infection.  A no-cost extension would also enable a summer visit by a student or the PI to Fort Pierce to perform additional sampling and tree assessments. 3. Please state budget status (underspend or overspend, and why):Budget spending is on track, considering delays due to COVID-19.  An amended budget by was developed and submitted in February, 2021. 


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