P-226 - Zymoseptoria-encoded Phytosulfokines: A novel mechanism for host manipulation?

Phytosulfokine (PSK) is perceived by LRR-RLKs, as shown in Arabidopsis, where it modulates salicylate and jasmonate pathways, conferring resistance to necrotrophic pathogens but susceptibility to biotrophic and hemibiotrophic pathogens. While well-studied in dicots, PSK signaling in monocots remains largely unexplored. However, we demonstrated its relevance in barley. Foliar PSK treatment of barley leaves followed by qRT-PCR revealed downregulation of HvPR1 and HvPAL3, suggesting immune modulation. Sequence analyses of effector repertoires from hemibiotrophic fungal pathogens in the genus Zymoseptoria identified a highly expressed, secreted protein containing the PSK motif YIYTQ. We investigated the function of this effector in Z. tritici (Zt) and Z. passerinii (Zpa), which infect wheat and barley, respectively. The PSK motifs in the effector ZtPSK are flanked by conserved putative KEX2 cleavage sites, suggesting possible processing of the effector into bioactive PSK. We hypothesize that Zymoseptoria produce PSK to manipulate host immunity. To test this, we aim to confirm the processing of fungal PSK by KEX2 in vitro. Additionally, we generated Zt and Zpa deletion mutants to investigate transcriptional and metabolic changes in the host during infection in presence and absence of ZtPSK. Our findings highlight a novel strategy of host immune manipulation by plant pathogens and provide deeper insights into the molecular mechanisms underlying Zymoseptoria infection.