Work

Histopathology of Aculeastrum americanum on Rubus idaeus and insights into the chloroplast-pathogen interaction

Year: 2025

Type: article

Abstract: Introduction Raspberry late leaf rust, caused by Aculeastrum americanum (Farl.) M. Scholler & U. Braun has been reported in several countries. All aerial parts of the plant can be infected, with the primary symptoms of this disease being powdery yellow spots. Lesions reduce leaf gas exchange and lead to early defoliation. Moreover, infected fruits become unmarketable, resulting in severe yield losses. Despite the growing threat of this rust, the histopathology of A. americanum on raspberry remains poorly understood, particularly on Rubus idaeus L., one of the widely cultivated and economically important raspberry species. Methods This study provides a detailed analysis of the infection, colonization, and reproduction processes of A. americanum on raspberry leaves, using light microscopy (bright field and fluorescence), confocal laser scanning microscopy, as well as scanning and transmission electron microscopy. Results and discussion Our findings provide the first microscopic evidence, in rust fungi, of the formation of two haustoria within a single host cell. Chloroplasts were observed in close association with the A. americanum haustorium, and underwent a series of alterations, that help to explain the drastic reduction in leaf gas exchange during late leaf rust infection. Although infected leaves produce defense substances, such as callose and phenolic compounds, raspberry leaves are unable to prevent successful colonization. The occurrence of cell collapses and necrosis, together with the ultrastructural alterations, likely contributes to the early defoliation observed in raspberry plants infected by A. americanum. This study provides novel insights into chloroplast-pathogen interactions, highlighting previously unrecognized aspects of chloroplast alterations during late leaf rust infection. Nevertheless, further investigations are required to deepen our understanding of this relationship in rust fungi as well as in other biotrophic pathogens.

Source: Frontiers in Plant Science

DOI: 10.3389/fpls.2025.1630100

Authors: Lucas Henrique Santos Barbosa, Ulla Neumann, Ton Timmers, Tonni Grube Andersen, Beatriz Appezzato-da-Glória

Institutions: Universidade de São Paulo, Max Planck Institute for Plant Breeding Research

Language: English

Topic: Yeasts and Rust Fungi Studies

Subfield: Molecular Biology

Field: Biochemistry, Genetics and Molecular Biology

Domain: Life Sciences

SDG: Zero hunger

Open Access status: gold

Estimated APC paid: $3,801