Deciphering a Half-Century Enigma: Unveiling the Role of Pathogenesis-Related Protein 1 (PR1) in Plant Immunity

A study has unraveled a mystery that persisted for fifty years in plant science – the elusive role of Pathogenesis-Related Protein 1 (PR1) in plant immunity. Led by Dr. Yet-Ran Chen at the Agricultural Biotechnology Research Center of Academia Sinica, this research casts a revealing light on the pivotal mechanism governing the enzymatic transformation of canonical immune biomarker PR1 into a potent CAPE cytokine. This transformation initiates plant systemic acquired resistance (SAR), a critical defense function against pathogenic infection. Remarkably, even plants incapable of synthesizing or perceiving salicylic acid, a central hormone for activating SAR, can activate systemic immunity when exposed to trace amounts of CAPE. This achievement serves as a foundation for enhancing crops' resilience against diseases and introduces novel perspectives for mitigating the adverse effects of global warming on plant immunity.
 

Published in Nature Communications (Aug.4, 2023). Article Access (https://www.nature.com/articles/s41467-023-40406-7).
 

When plants sense the invasion of pathogens, they rapidly trigger systemic and broad-spectrum defense responses to resist local infections and preemptively prevent the spread of pathogens to uninfected areas. The central of this defense mechanism is dependent on the biosynthesis and perception of salicylic acid, directly manifested on the PR1 gene/protein expression. PR1 is an early-discovered plant pathogenesis indicator molecule widely utilized for monitoring plant immune responses. However, since its discovery in 1970, the physiological functions and activities of PR1 in plant immune responses have remained a scientific mystery.
 

The significant breakthrough of this research is the successful determination of the physiological function and activity of PR1, confirming PR1 as the precursor protein of a highly active immune cytokine CAPE. In response to bacterial infections, plants must utilize a specific protease conducting caspase-like activity to release CAPE from PR1 to initiate systemic defense responses. We proposed the functional name of this enzyme as Enzyme Specific for CAPE Production (ESCAPE). This study further identifies XCP1 as the protein possessing ESCAPE function, with its enzymatic activity for CAPE production being highly temperature-sensitive. Importantly, plants lacking XCP1 cannot effectively activate systemic defense responses upon sensing a conserved molecular pattern from bacteria. Moreover, even when plants cannot synthesize or perceive salicylic acid, direct application of trace amounts of CAPE can still activate systemic defense responses in plants.


 

As salicylic acid serves as a central signaling role for plants to counteract pathogen attacks, many pathogens inhibit its mechanism in various ways to enhance their virulence. Recent reports also indicate that a warming climate directly affects the broad-spectrum defense response mediated by salicylic acid. Combining these findings with the present study, this phenomenon might be related to the thermo-sensitive activity of plant ESCAPE (XCP1). Therefore, the direct application of CAPE peptides or the optimization of mechanisms for CAPE production within plants could contribute to broadly enhancing defense capabilities against diseases. This research outcome holds vital implications for bolstering crop disease resistance and offers a new perspective for addressing the impact of global warming on plant immunity.

Ying-Lan Chen, Fan-Wei Lin, Kai-Tan Cheng, Chi-Hsin Chang, Sheng-Chi Hung, Thomas Efferth & Yet-Ran Chen (2023) Deciphering a Half-Century Enigma: Unveiling the Role of Pathogenesis-Related Protein 1 (PR1) in Plant Immunity Nature Communications, Aug.4, 2023