Methods to study PAMP-triggered immunity in Brassica species

The first layer of active defense in plants is based on the perception of pathogen-associated molecular patterns (PAMPs) leading to PAMP-triggered immunity (PTI). PTI is increasingly being investigated in crop plants, where it may have potential to provide durable disease resistance in the field. Limiting this work, however, is an absence of reliable bioassays to investigate PAMP responses in some species. Here, we present a series of methods to investigate PTI in Brassica napus. The assays allow measuring early responses such as the oxidative burst, mitogen-activated protein kinase phosphorylation, and PAMP-induced marker gene expression. Illumina-based RNA sequencing analysis produced a genome-wide survey of transcriptional changes upon PAMP treatment seen in both the A and C genomes of the allotetraploid B. napus. Later responses characterized include callose deposition and lignification at the cell wall, seedling growth inhibition, and PAMP-induced resistance to Pseudomonas syringae and Botrytis cinerea. Furthermore, using these assays, we demonstrated substantial variation in PAMP responses within a collection of diverse B. napus cultivars. The assays reported here could have widespread application in B. napus breeding and mapping programs to improve selection for broad-spectrum disease resistance.