# Pattern-triggered immunity in blue and white seed cultivars of Papaver somniferum

## TL;DR

This study explores how poppy plants defend against pathogens, identifying key immune responses and genes that could help breed more disease-resistant varieties.

## Contribution

The study provides the first comprehensive insights into pattern-triggered immunity (PTI) in poppy and identifies PsWRKY22 and PsPR2 as candidate marker genes.

## Key findings

- The peptide flg22 triggered strong immune responses, including ROS burst and growth inhibition in poppy cultivars.
- PsWRKY22 and PsPR2 were identified as reliable marker genes for monitoring PTI in poppy.
- Poppy plants showed low salicylic acid levels and no callose accumulation in response to flg22.

## Abstract

Papaver somniferum (poppy) is a traditional ingredient in Central and Eastern European cuisine and an important oilseed crop of the region. Since the main threat to stable poppy yield is pathogen infection, a detailed understanding of its defence mechanism is essential. The first robust layer of plant immunity, which plays a crucial role in combating pathogens, is pattern-triggered immunity (PTI). Here, we provide the first comprehensive insights into PTI in poppy. We selected four poppy varieties used in the food industry and investigated their response to various previously described peptide elicitors. Among all tested peptides, flg22 induced the most robust reactive oxygen species (ROS) burst, as well as triggering putative mitogen-activated protein kinase phosphorylation and seedling growth inhibition in all selected cultivars. We identified PsWRKY22 and PsPR2 as candidate marker genes suitable for monitoring poppy PTI responses. The tested poppy cultivars have low levels of salicylic acid. Callose accumulation was triggered by wounding but not by flg22. When studying PTI in plants, wounding is a challenge that needs to be considered, as it can obscure potential PTI responses. Our findings highlight conserved aspects of poppy immunity and the challenges of studying its PTI. The established pipeline facilitates improving our understanding of poppy immunity and has the potential for widespread application in breeding and improving selection for broad-spectrum disease resistance provided by enhanced PTI.

This study reveals how poppy plants activate immune defences against pathogens, focusing on pattern-triggered immunity (PTI). By testing four food-grade poppy varieties on the response to known immune-triggering peptides, we found that the peptide flg22 consistently activated robust immune responses, including oxidative bursts and growth inhibition. We identified two poppy genes, PsWRKY22 and PsPR2, as reliable markers of PTI. Interestingly, poppy plants showed low levels of salicylic acid and did not accumulate callose in response to flg22, highlighting unique aspects of poppy immunity. The findings offer a valuable framework for breeding poppy varieties with improved disease resistance.