# A cell wall extract of a Fusarium incarnatum strain requires the mitochondrial POLY(A)-SPECIFIC RIBONUCLEASE AtPARN for inducing cytoplasmic calcium elevation in Arabidopsis roots

## TL;DR

A fungal cell wall extract triggers calcium increases in plant roots, using a specific enzyme and signaling pathway.

## Contribution

Identifies AtPARN as a key component for calcium elevation in roots by Fusarium incarnatum extracts, independent of CORK1.

## Key findings

- Fusarium incarnatum extract induces calcium elevation in Arabidopsis roots via AtPARN, not CORK1.
- The response synergizes with cellotriose and chitin signaling pathways.
- Elevated calcium activates a mild defense response to balance fungal interactions.

## Abstract

Cytoplasmic Ca2+ ([Ca2+]cyt) elevation is a rapid response of roots to colonizing beneficial and pathogenic fungi. We have previously demonstrated that the elicitor-active compound cellotriose from a cell wall (CW) extract of the beneficial fungus Piriformospora indica requires the MALECTIN-DOMAIN CONTAINING CELLOOLIGOMER RECEPTOR KINASE1 (CORK1) and the mitochondrial POLY(A)-SPECIFIC RIBONUCLASE AtPARN for [Ca2+]cyt elevation in Arabidopsis roots. Here, we show that CW extracts from beneficial and pathogenic Fusarium strains, in particular Fusarium incarnatum strain K23, require AtPARN, but not CORK1 for [Ca2+]cyt elevation and the activation of Ca2+-dependent downstream responses. [Ca2+]cyt elevation by the F. incarnatum strain K23 extract does not require the BRASSINOSTEROID INSENSITIVE1-ASSOCIATED RECEPTOR KINASE1 (BAK1) co-receptor or the TWO-PORE Ca2+ CHANNEL1 (TPC1) but operates synergistically with the cellotriose- and chitin-induced signaling pathways. We propose a convergence of the signaling pathways induced by the CW extracts from P. indica and K23 at AtPARN prior to the increase in [Ca2+]cyt ~ 90 s after the stimulus. Furthermore, the elevated [Ca2+]cyt levels activate a mild defense response which might be used by the roots to restrict fungal propagation and to balance beneficial and non-beneficial traits in the symbiosis.

The online version contains supplementary material available at 10.1007/s12298-025-01600-7.