# Role of PMR4 and PDLP1 in priming of early acting penetration defense by resistance-inducing β-amino acids

## TL;DR

This study shows that two β-amino acids, RBH and BABA, prime plant cell wall defenses against a pathogen, but they use different molecular pathways.

## Contribution

The study reveals that BABA and RBH prime penetration resistance through distinct mechanisms involving PMR4 and PDLP1.

## Key findings

- BABA-primed defense relies on PDLPs and PMR4, while RBH-primed defense does not.
- PDLP1 over-expression mimics primed penetration resistance.
- BABA and RBH prime cell wall defenses via separate pathways.

## Abstract

R-β-homoserine (RBH) and β-aminobutyric acid (BABA) induce resistance against the oomycete Hyaloperonospora arabidopsidis (Hpa) in Arabidopsis, which is based on priming of multiple defense layers, including early acting penetration resistance at the cell wall. Here, we have examined the molecular basis of RBH- and BABA-primed defense by cell wall papillae against Hpa. Three-dimensional reconstruction of Hpa-induced papillae by confocal microscopy revealed no structural differences between control-, RBH-, and BABA-treated plants after Hpa challenge. However, mutations affecting POWDERY MILDEW RESISTANCE 4 or PLASMODESMATA LOCATED PROTEINs (PDLPs) only impaired BABA-induced penetration resistance and not RBH-induced penetration resistance. Furthermore, PDLP1 over-expression mimicked primed penetration resistance, while the intensity of GFP-tagged PDLP1 at germinating Hpa conidiospores was increased in BABA-primed plants but not RBH-primed plants. Our study reveals new regulatory layers of immune priming by β-amino acids and supports the notion that penetration resistance is a multifaceted defense layer that can be achieved through seperate pathways.

•The β-amino acids RBH and BABA prime cell wall defenses in Arabidopsis•BABA-primed cell wall defense relies on PDLPs and PMR4•BABA and RBH prime cell wall defense via different pathways and mechanisms

The β-amino acids RBH and BABA prime cell wall defenses in Arabidopsis

BABA-primed cell wall defense relies on PDLPs and PMR4

BABA and RBH prime cell wall defense via different pathways and mechanisms

Plant biology; Interaction of plants with organisms; Molecular plant pathology