Researchers have discovered the structure of a protein that allows the bacteria Pseudomonas syringae to interfere with the tomato plant’s immune system, causing bacterial speck disease.
The work helps explain how a bacterial pathogen has evolved to cause disease and may open the door to breeding tomato varieties resistant to speck disease, which has costly implications for tomato crops throughout the U.S.
The research — conducted at the Boyce Thompson Institute for Plant Science (BTI) in conjunction with scientists at Tsinghua University in Beijing — was published in the December issue of the journal Cell Host & Microbe.
“Our work presents clear evidence of a molecular arms race or coevolution between a host plant and a pathogen,” said Greg Martin, a scientist at BTI and lead author of the paper.
The paper describes the crystal structure of AvrPtoB – a protein injected into plant cells by Pseudomonas syringaethat interferes with the plant immune response and allows the bacteria to multiply. The paper also provides an understanding of how AvrPtoB binds and interferes with the plant protein BAK1, which acts with immune receptors to activate plant defenses.
Some tomato varieties are able to resist infection by Pseudomonas syringae because they express proteins, Fen and Pto, that detect AvrPtoB and mount a defense.
The structures characterized in Martin’s research revealed that two domains of AvrPtoB have a structural similarity, suggesting they arose from an ancestral avrPtoB gene. The paper also identifies part ofBAK1 that is structurally similar to the defense protein Pto.
Martin’s research is supported by the National Institutes of Health and the National Science Foundation.