Perception of the novel MAMP eMax from different Xanthomonas species requires the Arabidopsis receptor-like protein ReMAX and the receptor kinase SOBIR

As part of their innate immune system plants carry a number of pattern recognition receptors (PRRs) that can detect a broad range of microbe-associated molecular patterns (MAMPs). In a recently published article¹ we described a novel, proteinaceous MAMP termed eMax (enigmatic MAMP of Xanthomonas) that derives from Xanthomonas and gets recognized by the receptor-like protein ReMAX (RECEPTOR OF eMax) of Arabidopsis thaliana. ReMAX has no ortholog in Nicotiana benthamiana and this species does not respond to eMax even when transformed with ReMAX. However, interfamily transfer of eMax perception was successful with a chimeric form of ReMAX where the C-terminal part of the protein was replaced by the corresponding part of the tomato RLP EIX2 (ETHYLENE INDUCING XYLANASE2). In this addendum we describe the difficulties with the purification and identification of the MAMP eMax and we present data demonstrating that functionality of ReMAX, much like that of related RLPs, depends on the presence of the receptor kinase SOBIR (SUPPRESSOR OF BIR1–1).