Microbe-associated molecular pattern (MAMP)-triggered immunity (MTI) is the first layer of molecular defense encountered by pathogens when they attempt to infect plants. MTI is dependent on cell surface pattern-recognition receptors (PRR) which act upstream of mitogen-activated protein kinase (MAPK) pathways. Genetic screening and mutant knock-out lines have largely contributed to our knowledge of MTI. However, genetic screening is confined to phenotype-causing mutations and scarcely enables the discovery of redundantly-acting proteins. We sought to discover protein components that contribute in MTI, using a phenotype-independent approach to discern nucleus-localized proteins after MTI induction. We report on the nuclear proteome of Columbia-0 (Col-0) and chitin elicitor receptor kinase 1 (cerk1) mutant plants 15 min after MTI induction. Our approach revealed that MAMP-treated cerk1 plants had many proteins in common with Col-0-treated plants following chitosan treatment. cerk1 plants also manifested several unique proteins that were absent from Col-0 plants when elicited with chitosan indicating that they also perceive chitosan. Detailed analysis of the identified proteins revealed a nuclear accumulation of transcriptional regulators and transcription factors, DNA-modifying enzymes, RNA-binding proteins and ribosomal proteins. No novel MAPKs were found although Receptor for activated C kinase 1, a scaffold protein involved in defense, and a nucleotide binding leucine-rich repeat protein, implicated in resistance to Leptosphaeria maculans, were discovered in the nucleus of chitosan-treated plants and absent from water-treated control plants.