Emerging Insights into the Functions of Pathogenesis-Related Protein 1

Recent studies have shown that plant pathogenesis-related protein 1 (PR-1) family members bind sterols. This function is responsible for antimicrobial activity towards sterol auxotrophs such as Phytophthora species. However, the link between sterol binding and the proposed broader antimicrobial function of PR-1 remains unclear. PR-1 proteins harbour an embedded C-terminal peptide (CAPE) involved in plant immune signalling. Evidence suggests that CAPE has a signalling role that facilitates defence responses against microbial pathogens and also herbivores. The CAPE response is independent of other defence signalling pathways such as those elicited by recognised pathogen-associated molecular patterns. The significance of PR-1 proteins during plant–microbe interactions is now realised, with a growing list of identified pathogen effector proteins that directly interact with PR-1 during infection. The members of the pathogenesis-related protein 1 (PR-1) family are among the most abundantly produced proteins in plants on pathogen attack, and PR-1 gene expression has long been used as a marker for salicylic acid-mediated disease resistance. However, despite considerable interest over several decades, their requirement and role in plant defence remains poorly understood. Recent reports have emerged demonstrating that PR-1 proteins possess sterol-binding activity, harbour an embedded defence signalling peptide, and are targeted by plant pathogens during host infection. These studies have re-energised the field and provided long-awaited insights into a possible PR-1 function. Here we review the current status of PR-1 proteins and discuss how these recent advances shed light on putative roles for these enigmatic proteins. The members of the pathogenesis-related protein 1 (PR-1) family are among the most abundantly produced proteins in plants on pathogen attack, and PR-1 gene expression has long been used as a marker for salicylic acid-mediated disease resistance. However, despite considerable interest over several decades, their requirement and role in plant defence remains poorly understood. Recent reports have emerged demonstrating that PR-1 proteins possess sterol-binding activity, harbour an embedded defence signalling peptide, and are targeted by plant pathogens during host infection. These studies have re-energised the field and provided long-awaited insights into a possible PR-1 function. Here we review the current status of PR-1 proteins and discuss how these recent advances shed light on putative roles for these enigmatic proteins.