Phytohormone profiling reveals fungal signatures and strong manipulation of infection cycle in the Gymnosporangium juniper-virginianae dual-host plant system

The aim of this work was to examine the function of phytohormones in the pathogenesis of cedar-apple rust, a fungal disease caused by Gymnosporangium juniper-virginianae Schwein. on Eastern red cedar (Juniperus virginiana L.) and crabapple trees (Malus spp. Mill.). Control cedar branchlets, gall tissues, fungal telial horns, as well as healthy and infected apple leaves were collected throughout fungal and plant development and used for profiling endogenous cytokinins (CK) and abscisic acid (ABA) by high performance liquid chromatography – electrospray ionization – tandem mass spectrometry. Phytohormone composition implicates cytokinin involvement in the development of rust infection. Moreover, increased levels of total CKs, as well as the unique profiles of sporulating galls on cedar trees, telial horns, and infected apple leaves, dominated by cis-Zeatin type CK, suggest that the fungus can synthesize hormones to facilitate the infection process. Distribution of ABA in the fungal and plant tissues indicat...