Phylloxera (Daktulosphaira vitifolia) Utilizes Floral/Fruit Organ Developmental Genes As a Mechanism for Gall Formation on Leaves of Vitis

Molecular insights into the mechanisms underlying the complex relationship between grape phylloxera (Daktulosphaira vitifolia Fitch) and its host shows that the highly specialized galls induced on grape leaves may be as a result of the ectopic activation or redirection of flower and/or fruit development pathways via phytohormones. RNA sequencing and RT-PCR data collected from galled and un-galled tissues revealed changes in the expression of several key genes involved in floral/fruit development and hormone signaling, with LEAFY, the Vitis homologs that regulate the transition to flowering, WUSCHEL, which maintains the pluripotent stem cell pool in the shoot apical meristem and AGAMOUS, a carpel-identity gene, being some of the genes to increase in expression as galls develop and mature. Transgenic plants with targeted silencing of these genes were created to determine the correlation between changes in their expression and successful galling. Evaluation of transgenic selections of 'Seyval Blanc' (Vitis spp.), a susceptible hybrid cultivar, by direct challenge with D. vitifolia revealed plants showing increased resistance to phylloxera, and some exhibiting limited-to-no gall formation at all. This is an important step in understanding the insect's ability to manipulate plant morphogenesis in order to create such specialized structures. Controlling gene(s) identified via this knock-out approach can be modified to create phylloxera resistant cultivars.