Grape phylloxera (D. vitifoliae) manipulates SA/JA concentrations and signalling pathways in root galls of Vitis spp

Overcoming host defensive traits is a prerequisite to establish compatible plant-parasite interactions. Following parasite perception, jasmonic (JA) and salicylic acid (SA) signalling pathways mediate biotic stress signals resulting in the activation of host defence responses. Piercing-sucking grape phylloxera (Daktulosphaira vitifoliae) infests Vitis spp. by the formation of organoid root galls. This study aims to investigate whether host defensive SA/JA signalling pathways are affected during D. vitifoliae infestation. We hypothesize that the JA signalling pathway is induced during larval probing (14 hai). Compatible root gall formation (24 hai - 14 dai) involves the reduction of the JA, but the induction of the SA signaling pathway. T5C (V.berlandieri x V.riparia) cuttings are infested with a D. vitifoliae single founder lineage (biotype C). Phytohormone quantification (HPLC-MS) and transcriptional alterations of JA/SA marker genes (qRT-PCR) are determined in root tissues from larval probing (14 hai) until gall formation (>14 dai). Non-infested root tips are considered controls. Our results show a significant induction of all analysed JA marker genes during insect probing (14 hai), but their significant reduction during early gall formation (24 hai). Following gall formation (5-14 dai) SA and JA-Ile increase. However, only the analysed SA marker genes are induced, whereas JA marker gene expression levels are significantly reduced. Based on this data we conclude that the observed suppression of the JA signalling pathway might represent an important step for the compatible D. vitifoliae - Vitis spp. root interaction. We discuss whether the induced SA defences protect nutritive root galls against soil microbes.