# From roots to reproduction: the multifaceted roles of rapid alkalinization factor and epidermal patterning factor peptides in plants

## TL;DR

This review explores how RALF and EPF/EPFL peptides help plants grow, reproduce, and respond to stress by acting as signaling molecules.

## Contribution

The paper provides a comprehensive overview of the functional diversity and mechanisms of RALF and EPF/EPFL peptides in plants.

## Key findings

- RALF and EPF/EPFL peptides are involved in plant growth, development, and reproduction.
- These peptides play key roles in plant defense against biotic and abiotic stresses.
- They also contribute to plant–bacteria symbiosis and immune responses.

## Abstract

In plants, peptides play an irreplaceable role as intercellular communication molecules, triggering signal transduction by activating plasma membrane-localized receptors. Of specific interest here are the cysteine-rich peptides (CRPs), which are well-characterized for their disulfide bonds that enhance structural stability and functional specificity. Although the first CRP, systemin, was identified over three decades ago, our understanding of the evolutionary trajectories, functional diversity, and underlying mechanisms of CRPs remains limited. This review focuses on two main families of CRPs: the Rapid Alkalinization Factor (RALF) and the Epidermal Patterning Factor (EPF)/EPF-Like peptides. We thus explore the diverse and, so far, identified signalling pathways in which the peptides have a pivotal function. We organize our tour by providing a comprehensive overview of the discovery of peptides, structural diversity, and biological functions. Particularly, emphasis is placed on their roles in plant growth, development, reproduction, defence against biotic and abiotic stresses, and plant–bacteria symbiosis.

This review explores cysteine-rich peptides, specifically the RALF and EPF/EPFL families, in regulating growth, development, immune responses, and stress adaptation. It highlights recent mechanistic insights and challenges in peptide research.