Understanding the Role of Floral Genes in Gall Formation on Grape Leaves Caused by the Grape Phylloxera

The initiation and maintenance of the highly specialized galls on grape leaves induced by the grape phylloxera (Daktulosphaira vitifolia Fitch) has been proposed to be through the activation/redirection of flower and/or fruit development pathways via plant hormones. To gain molecular insights into the mechanisms underlying this complex insect–plant interaction, RNA sequencing data were generated from galled tissues in four stages and also from non-galled leaf tissue. The expression of several key genes involved in floral development and hormone signaling has been found to vary during gall development as compared to non-galled leaf tissue. Among these genes, noticeably include the Vitis homologs of a key gene regulating transition to flowering, LEAFY, and a carpel-identity gene, AGAMOUS. To fully understand their role in gall formation, antisense constructs to target and silence these floral genes were designed and introduced into a highly susceptible French-American hybrid Vitis spp. 'Seyval Blanc' via Agrobacterium-mediated transformation. A bidirectional dual promoter complex (BDDP) was used to simultaneously drive expression of the antisense target sequence and a selectable marker gene NPTII fused with a visual reporter gene enhanced fluorescent protein (EGFP), thus allowing for visual screening of transgenics. The use of transgenic plants with targeted silencing of floral genes will help demonstrate the correlation between successful galling and the changes in expression of such genes. The dependence of the insect's ability to initiate galls on the transition from vegetative to reproductive development through manipulation of these genes will be evaluated.