Oligogalacturonide production upon Arabidopsis thaliana–Botrytis cinerea interaction

Significance Oligogalacturonides (OGs), oligomers of α-1,4–linked galacturonic acid generated during plant infection by necrotrophic fungi, have been proposed to trigger plant basal immunity when they are applied exogenously to plant tissues. However, very little information exists on the structure and activity of the OGs that really accumulate during pathogen infection. This report reveals features of OGs generated during infection of Arabidopsis thaliana with the fungus Botrytis cinerea and identifies potential candidate OG elicitors. Despite an ever-increasing interest for the use of pectin-derived oligogalacturonides (OGs) as biological control agents in agriculture, very little information exists—mainly for technical reasons—on the nature and activity of the OGs that accumulate during pathogen infection. Here we developed a sensitive OG profiling method, which revealed unsuspected features of the OGs generated during infection of Arabidopsis thaliana with the fungus Botrytis cinerea. Indeed, in contrast to previous reports, most OGs were acetyl- and methylesterified, and 80% of them were produced by fungal pectin lyases, not by polygalacturonases. Polygalacturonase products did not accumulate as larger size OGs but were converted into oxidized GalA dimers. Finally, the comparison of the OGs and transcriptomes of leaves infected with B. cinerea mutants with reduced pectinolytic activity but with decreased or increased virulence, respectively, identified candidate OG elicitors. In conclusion, OG analysis provides insights into the enzymatic arms race between plant and pathogen and facilitates the identification of defense elicitors.