Molecular and functional characterization of two RGA type genes in the PdR1b locus for Pierce’s disease resistance in Vitis arizonica/ candicans

Authors: AGUERO, CECILIA - University Of California, Davis; Riaz, Summaira; TENSCHER, ALAN - University Of California, Davis; BISTUE, CAROLINA - University Of California, Davis; WALKER, M - University Of California, Davis

Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2022
Publication Date: 8/27/2022
Citation: Aguero, C.B., Riaz, S., Tenscher, A.C., Bistue, C., Walker, M.A. 2022. Molecular and functional characterization of two RGA type genes in the PdR1b locus for Pierce’s disease resistance in Vitis arizonica/ candicans. Plant Cell Tissue and Organ Culture. 151:497-510. https://doi.org/10.1007/s11240-022-02366-6.
DOI: https://doi.org/10.1007/s11240-022-02366-6

Interpretive Summary: The Pierce's disease (PD) resistance locus, PdR1b spans five disease resistance genes, belonging to the Leucine-Rich Repeat Receptor Kinase gene family. Two of these genes, V.ari-RGA14 and V.ari-RGA18 were used to develop constructs with native promotors and transform V. vinifera cultivars Chardonnay (CH) and Thompson Seedless (TS) and V. rupestris St George (SG). Results indicated reduced symptoms in transgenic lines of Chardonnay and improved regrowth in rootstock St. George with lower bacterial titer and lower expression of pectin lyase and beta 1-3 glucanase 3 gene.

Technical Abstract: Pierce’s disease is a deadly disease of grapevines caused by the bacterial pathogen Xylella fastidiosa (Xf). A Pierce’s Disease resistance locus from Vitis arizonica/candicans b43-17 segregated as a single dominant gene and mapped as PdR1a and PdR1b in two F1 sibling selections. The physical mapping of the PdR1b allele allowed the identification of five ORFs of the Leucine-Rich Repeat Receptor Kinase gene family. Two ORFs: V.ari-RGA14 and V.ari-RGA18 were used to transform embryogenic callus of V. vinifera Chardonnay (CH) and Thompson Seedless (TS) and V. rupestris St George (SG) via Agrobacterium tumefaciens. Regenerated plants were inoculated with Xf under greenhouse conditions. Genetic transformation with RGA14 and 18 did not generate resistance in CH and TS, although some lines of CH showed significantly lower stem bacterial concentration and/or several exhibited reduced symptoms. In transgenic SG-14, improved regrowth was accompanied with lower bacterial titers and decreased pectin lyase and beta 1-3 glucanase 3 gene expression. The limited effects of the transgenes on PD resistance could be explained by the lack of suitable partners or the presence of susceptibility factors that can’t be overcome in vinifera/rupestris genetic backgrounds under the experimental conditions used in this research. The involvement of RGA-17 in b43-17 resistance to Xf should not be discarded.