Heterologous expression of Arabidopsis FLS2 in Nicotiana benthamiana confers responsiveness to Ralstonia flg22 and activation of anti-bacterial immunity.

The association between Arabidopsis FLS2 and BAK1/SERK3 triggered by bacterial flagellin is the best-studied example of plant PRR receptor/co-receptor complex. Although most plants are able to perceive the flagellin epitope flg22 from most bacterial species, certain pathogens, such as Agrobacterium tumefaciens or Ralstonia solanacearum, have evolved polymorphisms in their flg22 sequence, avoiding perception by most plants tested so far. Specific plant species, such as Vitis riparia or Glycine max, respectively, have subsequently evolved FLS2 versions with the ability to recognize these polymorphic flg22 peptides. The model plants Arabidopsis or N. benthamiana are not able to perceive the flg22 peptide from R. solanacearum (flg22^Rso). However, in this work, we found that the expression of AtFLS2 in N. benthamiana confers responsiveness to flg22^Rso, leading to the activation of specific downstream responses. AtFLS2 interacts with the BAK1 orthologs in N. benthamiana (NbSERKs), which contribute to flg22^Rso recognition by AtFLS2 and subsequent immune responses. Finally, we found that this recognition activates anti-bacterial immunity that restricts Ralstonia growth, suggesting that cross-species PRR-co-receptor compatibility could be exploited for the development of tailored immunity against pathogens with polymorphic PAMPs.