Reactive oxygen species generated in chloroplasts contribute to tobacco leaf infection by the necrotrophic fungus Botrytis cinerea

Abstract

SUMMARYReactive oxygen species (ROS) play fundamental roles in plant responses to pathogen infection, including modulation of cell death processes and defense-related gene expression. Cell death triggered as part of the hypersensitive response enhances resistance to biotrophic pathogens, but favors the virulence of necrotrophs. Even though the involvement of ROS in the orchestration of defense responses is well established, the relative contribution of specific subcellular ROS sources to plant resistance against microorganisms with different pathogenesis strategies is not completely known. The aim of this work was to investigate the role of chloroplastic ROS in plant defense against a typical necrotrophic fungus, Botrytis cinerea. For this purpose, we used transgenic Nicotiana tabacum (tobacco) lines expressing a plastid-targeted cyanobacterial flavodoxin (pfld lines), which accumulate lower chloroplastic ROS in response to different stresses. Tissue damage and fungal growth were significantly reduced in infected leaves of pfld plants, as compared with infected wild-type (WT) counterparts. ROS build-up triggered by Botrytis infection and associated with chloroplasts was significantly decreased (70-80%) in pfld leaves relative to the wild type. Phytoalexin accumulation and expression of pathogenesis-related genes were induced to a lower degree in pfld plants than in WT siblings. The impact of fungal infection on photosynthetic activity was also lower in pfld leaves. The results indicate that chloroplast-generated ROS play a major role in lesion development during Botrytis infection. This work demonstrates that the modulation of chloroplastic ROS levels by the expression of a heterologous antioxidant protein can provide a significant degree of protection against a canonical necrotrophic fungus.

Chloroplasts and Plant Immunity: Where Are the Fungal Effectors?

“…Several photosynthetic parameters, such as maximum quantum yield, photosynthetic performance index and electron transfer efficiency, were inhibited to a lesser degree in plants expressing flavodoxin. Furthermore, wild-type plants showed fewer intact active reaction centers of the PSII per leaf area compared to the flavodoxin-expressing lines [34]. Phytoalexin accumulation was also reduced in the infected plants expressing flavodoxin, and the expression of plant defense genes, such as glucanases, chitinases or PR1, was delayed compared to wild-type plants.…”

“…The transgenic plants infected with B. cinerea showed less tissue damage and reduced fungal growth as well as changes in photosynthetic activity and plant defense responses [34]. In particular, mycelial growth was reduced by 67-90% in the transgenic plants expressing the cyanobacterial flavodoxin protein compared to wild-type plants during a time course of infection [34]. Several photosynthetic parameters, such as maximum quantum yield, photosynthetic performance index and electron transfer efficiency, were inhibited to a lesser degree in plants expressing flavodoxin.…”

“…ROS generated in chloroplasts is a major contributor to plant immunity. For example, the expression of a cyanobacterial chloroplast-targeted flavodoxin (which reduces ROS accumulation) in transgenic tobacco reduced the symptoms of infection by the necrotrophic fungus Botrytis cinerea or the hemibiotrophic bacterium X. campestris [34][35][36]. The transgenic plants infected with B. cinerea showed less tissue damage and reduced fungal growth as well as changes in photosynthetic activity and plant defense responses [34].…”

“…For example, the expression of a cyanobacterial chloroplast-targeted flavodoxin (which reduces ROS accumulation) in transgenic tobacco reduced the symptoms of infection by the necrotrophic fungus Botrytis cinerea or the hemibiotrophic bacterium X. campestris [34][35][36]. The transgenic plants infected with B. cinerea showed less tissue damage and reduced fungal growth as well as changes in photosynthetic activity and plant defense responses [34]. In particular, mycelial growth was reduced by 67-90% in the transgenic plants expressing the cyanobacterial flavodoxin protein compared to wild-type plants during a time course of infection [34].…”

Chloroplast‐targeted antioxidant protein protects against necrotrophic fungal attack

“…The Carrillo group previously showed (Zurbriggen et al, 2009) that expressing a chloroplast-targeted flavodoxin (Fld) specifically reduced plastid-generated ROS and consequently inhibited LCD upon inoculation with a hemi-biotrophic bacterial pathogen, Xanthomonas campestris, albeit a non-host interaction where infection wasn't expected. In this highlighted article (Rossi et al, 2017), the groups of N estor Carrillo and Fernando Pieckenstain demonstrate that this Fld approach is effective against a necrotrophic fungus, Botrytis cinerea.…”