Identification of the Functional Domains of Arabidopsis FLS2

Abstract

Arabidopsis FLS2 is a leucine-rich repeat (LRR) transmernbrane receptor-kinase that recognizes bacterial flagellin and induces plant innate immune responses. Flg22 is a 22 amino acid peptide based on a sequence of flagellin that is highly conserved among bacteria. FLS2 directly binds flg22 and then elicits plant defense responses. A set of residues in the FLS2-LRR domain were chosen for study based on their degree of evolutionary conservation among FLS2 proteins from diverse Brassicaceae species. These residues were examined using site-directed mutagenesis to identify the functional regions ofFLS2. Surprisingly, none of these mutations strongly disrupted FLS2 function. This is in contrast to the significant impacts on defense that have been observed with some mutations in the ~-strand/~-tum region of the FLS2-LRR. Additionally, putative N-glycosylation sites were disrupted to determine the role of glycosylation in the structure and/or function ofFLS2. 16 of the 17 mutations did not strongly disrupt FLS2 function, suggesting that these are not crucial N-glycosylation sites. One of these 17 mutations was found to cause decreased flg22 response and abnormal FLS2 expression. The LRR structural motif is common in plant immune receptors, and also in mammalian immune systems and proteins that control other aspects of growth and development, making knowledge about protein interactions involving LRRs beneficial both for plant and mammalian systems.