Plant Peptide Signals


Over the past 25 years, knowledge of plant peptide signalling has expanded and recent discoveries have allowed us to understand several mechanisms underpinning their action. It is becoming clear that cell–cell communication mediated by peptide signalling is integral to many plant processes. This article focusses on the best‐studied areas of plant peptide signalling. We discuss two major families of plant peptides that function during plant development; the CLAVATA3/endosperm surrounding region (CLE) peptide family, which regulate cell differentiation and division at the shoot apical meristem (SAM), root apical meristem (RAM) and in the vasculature and the epidermal patterning factor‐like (EPFL) family of signalling peptides that regulate stomatal development and patterning. We also discuss peptides that regulate self‐incompatibility, and the role of the peptide phytosulfokine during plant growth, pollen tube growth and guidance and pathogen infection.

Key Concepts

  • Plant peptides regulate development and stress response.
  • The CLE family of peptides regulate cell differentiation and division at the shoot apical meristem (SAM), root apical meristem (RAM) and in the vasculature.
  • The epidermal patterning factor‐like (EPFL) family of signalling peptides that regulate stomatal development and patterning.

Keywords: peptide signal molecules; signal peptide; leucine‐rich repeat; receptor kinase; Arabidopsis; stomatal development; phytosulfokine

Figure 1. A cross section of an Arabidopsis shoot apical meristem (SAM). (a) The SAM has two surface layers (L1 and L2) known as the tunica. Cells within the tunica show anticlinal division planes. Underneath the tunica lies the corpus (L3). Cells within the corpus divide in all planes preventing the formation of a defined layering. Cells of the different layers of the SAM have different cell fates. Cells found within L1 form epidermal cells of shoots, leaves and flowers. Cells within L2 form ground tissue and germ cells, and cells within L3 form the vascular tissue of the stem and internal tissue of the leaf and flower. (b) The SAM is also divided into distinct zones overlying the cell layers. The central zone (CZ) exists at the tip of the SAM and contains the stem cell population. Underneath the CZ lies the organising centre (OC). The peripheral zone (PZ) and rib zone (RZ) surround the CZ. Stem cells within the CZ divide and supply the PZ and RZ with cells that differentiate and are incorporated into aerial organs (e.g. leaves and flowers) and the core of the stem, respectively. (c) clavata mutants show enlargement of the SAM apex. This is caused by an expansion of the central zone (CZ) due to increased amounts of stem cells. Increased organ generation can occur in clv mutants owing to the greater abundance of stem cells.
Figure 2. (a) The CLV3/WUS feedback loop within the shoot apical meristem (SAM) of wild‐type Arabidopsis. A signal mediated by WUS expression in the organising centre (OC) confers stem cell identity to the overlying cells in the central zone (CZ). The stem cells of the CZ negatively regulate WUS expression via a CLV3‐mediated pathway. This maintains a stable stem cell population size. (b) The CLV3 signal binds to CLV1 receptors on the surface of cells within the organising center (OC). There is mixed evidence to whether CLV2/CRN and RPK2 receptor complexes can directly bind CLV3. Recent research suggests that they do not and may function as co‐receptors or recognise other CLE ligands. The binding of CLV3 induces downstream signalling pathways that mediate WUS repression.
Figure 3. Developmental progression from meristemoid mother cell (MMC) through to a fully developed stomata. EPF2 and EPF1 expression in co‐ordination with their co‐receptors ERECTA, ERECTA like 1 (ERL1) and ERECTA like 2 (ERL2) expression regulate stomatal development at distinct stages. EPF2 expression is indicated by the pale purple shading, while EPF1 expression is shown by the pale red shading. EPF2 and ERECTA expression is shown to be the strongest in protodermal and stomatal precursor cells such as meristemoids (M). Later during development EPF1 expression dominates in the guard mother cells (GMCs) and the guard cells (GCs), the expression of EPF1 coincides with EERCTA like 1 and ERECTOR like 2 receptor expression. The final stage depicts a secondary meristemoid (SM) cell, at this stage, we see the expression of both EPF1 and EPF2. Here, the expression of EPF1 is preventing cells in direct contact with GCs from differentiating into GCs (enforcing stomatal spacing).
Figure 4. Amino acid sequences of (a) PSK and (b) Arabidopsis PSK precursors.


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Further Reading

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Dutton, Chris, Pridgeon, Ashley, and Gray, Julie E(Jan 2016) Plant Peptide Signals. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0020110.pub2]