The sieve-element endoplasmic reticulum: A focal point of phytoplasma-host plant interaction?

Rita Musetti; Laura Pagliari; Giovanni Mian; Fernando R De Oliveira Cantao; Chiara Bernardini; Simonetta Santi; Aart J E van Bel

doi:10.3389/fmicb.2023.1030414

The sieve-element endoplasmic reticulum: A focal point of phytoplasma-host plant interaction?

Front Microbiol. 2023 Feb 2:14:1030414. doi: 10.3389/fmicb.2023.1030414. eCollection 2023.

Authors

Rita Musetti¹, Laura Pagliari², Giovanni Mian², Fernando R De Oliveira Cantao², Chiara Bernardini², Simonetta Santi², Aart J E van Bel³

Affiliations

¹ Department of Land, Environment, Agriculture and Forestry (TESAF), Università di Padova, via dell' Università, Legnaro, Italy.
² Department of Agricultural, Food, Environmental and Animal Sciences, University of Udine, via delle Scienze, Udine, Italy.
³ Institute of Phytopathology, Justus-Liebig University, Giessen, Germany.

Abstract

The rough endoplasmic reticulum (r-ER) is of paramount importance for adaptive responses to biotic stresses due to an increased demand for de novo synthesis of immunity-related proteins and signaling components. In nucleate cells, disturbance of r-ER integrity and functionality leads to the "unfolded protein response" (UPR), which is an important component of innate plant immune signalling. In contrast to an abundance of reports on r-ER responses to biotic challenges, sieve-element endoplasmic reticulum (SE-ER) responses to phytoplasma infection have not been investigated. We found that morphological SE-ER changes, associated with phytoplasma infection, are accompanied by differential expression of genes encoding proteins involved in shaping and anchoring the reticulum. Phytoplasma infection also triggers an increased release of bZIP signals from the (SE-ER)/r-ER and consequent differential expression of UPR-related genes. The modified expression patterns seem to reflect a trade-off between survival of host cells, needed for the phytoplasmic biotrophic lifestyle, and phytoplasmas. Specialized plasmodesmata between sieve element and companion cell may provide a corridor for transfer of phytoplasma effectors inducing UPR-related gene expression in companion cells.

Keywords: Arabidopsis; endoplasmic reticulum; phytoplasma; phytoplasma-host interaction; pore-plasmodesma units; sieve element; sieve-element ER docking sites; unfolded protein response.