The jasmonate receptor COI1 is required for AtPep1-induced immune responses in Arabidopsis thaliana

External jasmonic acid isoleucine mediates amplification of plant elicitor peptide receptor (PEPR) and jasmonate-based immune signalling

Jasmonic acid-isoleucine (JA-Ile) is a plant defence hormone whose cellular levels are elevated upon herbivory and regulate defence signalling. Despite their pivotal role, our understanding of the rapid cellular perception of bioactive JA-Ile is limited. This study identifies cell type-specific JA-Ile-induced Ca2+ signal and its role in self-amplification and plant elicitor peptide receptor (PEPR)-mediated signalling. Using the Ca2+ reporter, R-GECO1 in Arabidopsis, we have characterized a monophasic and sustained JA-Ile-dependent Ca2+ signature in leaf epidermal cells. The rapid Ca2+ signal is independent of positive feedback by the JA-Ile receptor, COI1 and the transporter, JAT1. Microarray analysis identified up-regulation of receptors, PEPR1 and PEPR2 upon JA-Ile treatment. The pepr1 pepr2 double mutant in R-GECO1 background exhibits impaired external JA-Ile induced Ca2+ cyt elevation and impacts the canonical JA-Ile responsive genes. JA responsive transcription factor, MYC2 binds to the G-Box motif of PEPR1 and PEPR2 promoter and activates their expression upon JA-Ile treatment and in myc2 mutant, this is reduced. External JA-Ile amplifies AtPep-PEPR pathway by increasing the AtPep precursor, PROPEP expression. Our work shows a previously unknown non-canonical PEPR-JA-Ile-Ca2+ -MYC2 signalling module through which plants sense JA-Ile rapidly to amplify both AtPep-PEPR and jasmonate signalling in undamaged cells.

Damage-Associated Molecular Patterns and Systemic Signaling

Cellular damage inflicted by wounding, pathogen infection, and herbivory releases a variety of host-derived metabolites, degraded structural components, and peptides into the extracellular space that act as alarm signals when perceived by adjacent cells. These so-called damage-associated molecular patterns (DAMPs) function through plasma membrane localized pattern recognition receptors to regulate wound and immune responses. In plants, DAMPs act as elicitors themselves, often inducing immune outputs such as calcium influx, reactive oxygen species generation, defense gene expression, and phytohormone signaling. Consequently, DAMP perception results in a priming effect that enhances resistance against subsequent pathogen infections. Alongside their established function in local tissues, recent evidence supports a critical role of DAMP signaling in generation and/or amplification of mobile signals that induce systemic immune priming. Here, we summarize the identity, signaling, and synergy of proposed and established plant DAMPs, with a focus on those with published roles in systemic signaling.

Enhancing potato resistance against root-knot nematodes using a plant-defence elicitor delivered by bacteria

The root-knot nematode Meloidogyne chitwoodi is a pest that affects potato production in the Pacific Northwest of the United States. Here, to develop new strategies against M. chitwoodi infection of potato, we engineered Bacillus subtilis to secrete the plant-defence elicitor peptide StPep1. Pre-treatment of potato roots with the bacteria secreting StPep1 substantially reduced root galling, indicating that a bacterial secretion of a plant elicitor is an effective strategy for plant protection.

Modulation of plant innate immune signaling by small peptides

Small peptides regulate the cellular coordination of growth, development, and stress tolerance in plants. In addition to direct antimicrobial activities, small secreted peptides have emerged as key signaling molecules in the plant immune response. Here, we highlight recent discoveries of several small peptides that amplify and fine-tune immune signaling.