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Poster: Biology & Disease Mgmt: Bacteriology


Phenotypic effects of anti-Candidatus Liberibacter asiaticus antibody expression in grapefruit
T. MCNELLIS (1), T. Gottwald (2), J. Sinn (1), V. Orbovic (3) (1) Penn State University, U.S.A.; (2) USDA ARS, U.S.A.; (3) CREC-University of Florida, U.S.A.

Citrus greening, or huanglongbing (HLB), is a globally-important, fatal citrus disease caused by the gram-negative, phloem-limited bacterium “Candidatus Liberibacter asiaticus” (CLas). HLB-resistant citrus germplasm is not available. This project aims to develop HLB-resistant grapefruit. Based on homology to Xylella fastidiosa and E. coli, the CLas NodT outer membrane transporter might export factors required for virulence. The goal of this project is to block NodT-mediated virulence factor export, potentially disrupting CLas virulence. A single-chain antibody (scFv) directed at the major predicted extracellular loop of CLas NodT was expressed in stably transformed ‘Duncan’ grapefruit. To promote protein expression, stability and mobility in the phloem, the antibody was fused to the phloem-mobile Flowering Locus T (FT) protein. Full-length, stable FT-scFv protein was expressed in multiple transgenic lines, most of which had no phenotypic abnormalities. Thus, FT-antibody fusion protein can be expressed in citrus without deleterious effects on plant development. However, the highest expressing line exhibited precocious flowering and fruit set, presumably due to the bloom-inducing activity of the FT domain. This suggests that sufficiently high FT-scFv expression triggers flowering, which could be useful in developing rapid-flowering citrus lines to expedite breeding. The HLB resistance status of the FT-scFv grapefruit lines is now being determined.