Abstract
Lipopolysaccharide (LPS), which is a primary constituent of the outer membrane of gram-negative bacteria, is a pathogen-associated molecular pattern. Although LPS causes defense-related responses in plants, none of the molecules consisting of the LPS recognition mechanism have been identified. We focused on human LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI), which can bind to LPS directly and regulate the physiological responses to LPS. Arabidopsis has two LBP/BPI-related genes (AtLBPs). We investigated their function on LPS-induced plant defense responses.
We demonstrated the direct binding between recombinant proteins of AtLBPs and LPS. After LPS treatment, AtLBP2 mutants showed the earlier initiation of pathogenesis-related 1 gene expression than wild-type. Furthermore, AtLBP2 mutants showed callose deposition with a lower concentration of LPS. Thus, AtLBP2 mutants exhibited higher sensitivity to LPS than wild-type, suggesting that AtLBP2 play an important role in negative regulation of LPS-induced signal transduction.
