Lipopolysaccharide Induces The Production Of Reactive Oxygen Species In Chloroplasts

When pathogens infect plants,plants first recognize some of the conserved structures of pathogens,called the Microbe-Associate Molecular Patterns(MAMPs).Lipopolysaccharide(LPS),known as endotoxin,is a major component of the gram-negative bacterial outer membrane.As a typical MAMPs,LPS induces innate immune response in animals and can cause sepsis and endotoxic shock in severe cases,a disease with high mortality in the immergency room.In plants,LPS is also considered as an important MAMPs,and the recognition of LPS by the receptor kinase Lipooligosaccharide-Specific Reduced Elicitation(LORE)in Arabidopsis thaliana can induce typical innate immune responses.However,other than LORE,LPS recognition signaling transduction and the immune responses are still unclear.In this study,we found that LPS can trigger a biphasic production of Reactive Oxygen Species(ROS)in A.thaliana.The first was a brief,rapid ROS burst similar to that induced by the bacterial flagellin(flg22),while the second,slow and long-lasting burst was LPS specific.Microscopic observation results showed that the second ROS burst was closely related to chloroplasts.In addition,LPS-triggered chloroplast ROS burst is only partially dependent on the LORE receptor,suggesting that other receptors,in addition to LORE,might be required for LPS-triggered chloroplast ROS in Arabidopsis.To identify the LPS receptors and other downstream signaling components in plants,we performed a genetic mutant screen in the EMS(Ethyl Methyl Sulfone)mutagenized mutant population,and isolated mutants Defective in LPS-triggered late-ROS(delt).So far we have screened 15,000 EMS mutagenized Arabidopsis plants and obtained 200 LPS insensitive mutants,then we select 10 mutants,delt1-delt10,of which delt3 mutant was further analyzed.Backcross analysis showed that DELT3 is a single recessive mutation.Combined with the map-based cloning and genome-wide sequencing,we identified the DELT3 gene mapped to 973257bp?5612989bp interval of the fourth chromosome.Future work will further fine-tune the DELT3 gene and explain how DELT3 functions as a signaling component of LPS-induced late ROS burst in Arabidopsis.This study is of great significance in cultivating a broad spectrum of sustainable disease-resistant cultivars in agriculture.