Study on pathogen associated molecular patterns that cause plant immune responses

Abstract

Flagellin from the rice avirulent N1141 strain of Acidovorax avenae, functions as a pathogen-associated molecular pattern （PAMP） and induces PAMP-triggered immunity （PTI） in rice.　To study the recognition mechanism of flagellin in rice, the region（s） definition of the flagellin protein required to activate the PTI response was attempted.　Among four fragments of N1141 flagellin, the C-terminal CD2-1 fragment induced PTI responses in cultured rice cells.　Synthetic flg22, which is sufficient to produce the flagellin response in Arabidopsis elicited no immune responses in rice.　In addition, CD2-1 triggered resistance to coinfection with pathogenic bacteria.　Taken together, these data suggest that rice mainly recognizes flagellin CD2-1, and that this epitope recognition leads to PTI responses.　To identify additional PAMPs from A. avenae N1141, cell extracts were isolated from flagellin-deficient N1141.　The cell extracts still induced PTI responses, suggesting that flagellin-deficient N1141 possesses an additional PAMP distinct from flagellin.　We showed that elongation factor Tu （EF-Tu）, one of the most abundant bacterial proteins, act as a PAMP in rice and causes several PTI responses.　Synthetic elf18, which is sufficient to produce the EF-Tu response in Arabidopsis, did not cause any immune responses in rice, whereas an EF-Tu middle region comprising Lys176 to Gly225, termed EFa50, is fully active as a PAMP in rice.　These data demonstrate that rice recognizes EFa50, which is distinct from elf18, and that this epitope induces PTI re­sponses.