The short chitooligosaccharide CO4 inhibits chitin-triggered immunity in grapevine and promotes the infection by Botrytis cinerea but not Plasmopara viticola.

Plants have developed strategies to detect different microorganisms and specifically modulate their immune responses. A primary recognition involves the perception of highly conserved molecular signatures, also known as microbe-associated molecular patterns (MAMPs). Among them, chitin, the main component of the fungal cell wall, is well known to be particularly active in triggering immunity in many plant species, including grapevine. While chitin is a well-known elicitor of plant defenses, other MAMPs such as short chitooligosaccharides [e.g. chitotetraose (CO4)] and lipo-chitooligosaccharides (LCOs) have been described to promote symbiotic interactions and inhibit plant immunity in several plant species. Here, we analyzed the molecular signaling triggered by these MAMPs in grapevine, focusing on two key immune responses: phosphorylation of mitogen-activated protein kinases (MAPKs) and expression of defense genes. Our results revealed that CO4 is the most active MAMP to inhibit some immune responses normally triggered by chitin. In addition, CO4 pre-treatment of grapevine leaves resulted in the repression of immune responses and increased susceptibility to the fungal pathogen Botrytis cinerea while showing no effect on Plasmopara viticola infection. These results suggest that grapevine can regulate its immune signaling pathways differently to either block or promote microbial colonization, depending on the MAMP perceived.