Plants have two basic immune pathways. First, a pattern recognition receptor (PRR) on the plant cell’s surface recognizes pathogen-associated molecular patterns (PAMPs) released by invaders—say, the flagellar proteins from pathogenic bacteria. This jump-starts signaling pathways inside the cell that spur the production of reactive oxygen species (ROS) and antimicrobial compounds, which are secreted to combat the pathogen. PAMP-triggered pathways can also lead to changes in gene expression and hormone levels.

But bacteria can interfere with PAMP-triggered immunity by injecting effector molecules into the plant cell. Intracellular plant protein complexes called nucleotide-binding domain, leucine-rich repeat receptors (NLRs) bind bacterial effectors and set off secondary immune cascades that boost the PAMP-triggered responses. NLR-binding can also lead to plant cell death, limiting the infection.

© THOM GRAVESPlant immune systems must integrate a diversity of factors to successfully fight off pathogens
without harming the plant. Defense-related changes in hormone signaling, for example,...



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