An uORF-encoded mobile peptide sparks systemic stomatal immunity

Area of Science:

• Plant immunity
• Plant signaling
• Molecular plant pathology

Background:

• Plants possess defense mechanisms, including stomatal closure, to prevent pathogen entry.
• Systemic responses are crucial for whole-body defense against external stimuli.
• The mobile signals mediating systemic stomatal immunity (SSIM) in plants were previously unknown.

Purpose of the Study:

• To identify the mobile signals responsible for transmitting pathogen-induced danger signals.
• To elucidate the molecular mechanism of systemic stomatal immunity (SSIM).
• To characterize the role of a novel peptide in long-distance plant defense signaling.

Main Methods:

• Observation of pathogen-infected local and distal systemic leaves.
• Identification and characterization of a novel mobile peptide, upstream open reading frame (uORF)-encoded systemic stomatal immune conductor (USIC).
• Analysis of the USIC receptor complex (SUCROSE-INDUCED RECEPTOR KINASE 1 (SIRK1)-KINASE 7 (KIN7)) and downstream signaling pathways involving METACASPASE 4 (MC4).

Main Results:

• Pathogen infection triggers an increase in USIC in local leaves, which is secreted into the apoplast for transport.
• USIC is perceived by the SIRK1-KIN7 receptor complex in systemic leaves, leading to KIN7 cleavage.
• KIN7 regulates stomatal closure through association with proton pumps and aquaporins, mediating SSIM.

Conclusions:

• A uORF-encoded peptide, USIC, acts as a long-distance mobile signal inducing systemic stomatal immunity (SSIM).
• The SIRK1-KIN7 receptor complex and MC4-mediated KIN7 cleavage are critical components of the SSIM pathway.
• This study reveals a novel mechanism of systemic plant defense involving mobile peptide signaling.