P-221 - Dysfunction of the ER and Golgi network caused by loss-of-function of BnHVA22c and BnCRT1a reduces the susceptibility of oilseed rape (Brassica napus) to fungal infection (Verticillium longisporum).

Verticillium longisporum (Vl43) is a soil-borne fungal pathogen that causes stem stripe in oilseed rape (OSR) and severe yield losses. HVA22c and CRT1a are endoplasmic reticulum proteins. Both genes are up-regulated by Vl43 infection. We knock them out in OSR by CRISPR/Ca to investigate their role in plant-fungus interaction. Both loss of function mutants showed significantly reduced susceptibility to Vl43 infection with impaired disease symptoms compared to wild-type ones. The loss of function of both genes drastically altered the transcriptomic landscape, downregulating many genes involved in ER function but enhancing plants' ethylene (ET) signalling. Many genes related to plant immune responses were highly up-regulated, including genes for MPK3 and its substrates ACS2, ACS6 and WRKY33. Several PR and PDF proteins, calcium-dependent serine/threonine kinases, and genes for oxidative bursts (RBOHD), plant cell wall strengthening (CCoAOMT1, EXT3) and pathogen viability reduction (CHI, OSM34) were also enhanced in the mutants. Furthermore, we demonstrate that HVA22c and CRT1a are functionally required for a fully compatible plant-fungus interaction. The reduced susceptibility to Vl43 is due to an impaired ER-dependent functionality of the fungal effectors and enhanced plant immunity by, e.g. activating MPK3 signalling. The potential of CRISPR/Cas9 targeting ER proteins to improve plant disease resistance and the function of ER and ER proteins in plant immunity are discussed.