Ethylene signalling is essential for the resistance of Nicotiana attenuata against Alternaria alternata and phytoalexin scopoletin biosynthesis

Abstract

The phytohormone ethylene plays an important role in plant defence responses to pathogen attack. When infected by the necrotrophic fungal pathogen Alternaria alternata (tobacco pathotype), which causes severe diseases in Nicotiana species, the wild tobacco plant Nicotiana attenuata accumulates a high amount of the jasmonate (JA)‐dependent phytoalexin scopoletin to defend itself against this fungal pathogen. However, it is still not known whether ethylene signalling is also involved in scopoletin biosynthesis and the resistance of N. attenuata. After infection, ethylene biosynthetic genes were highly elicited. Furthermore, plants strongly impaired in ethylene biosynthesis or perception had dramatically decreased scopoletin levels, and these plants became more susceptible to the fungus, while A. alternata‐elicited JA levels were increased, indicating that the decreased defence responses were not due to lower JA levels. Thus, it is concluded that after infection, ethylene signalling is activated together with JA signalling in N. attenuata plants and this subsequently regulates scopoletin biosynthesis and plant resistance.

Capsidiol, a defensive sesquiterpene produced by wild tobacco in response to attack from the fungal pathogenAlternaria alternata, is regulated by an ERF2-like transcription factor

“…In contrast to the observation in N. benthamiana inoculated with P. infestans , our experiments did not support the role of ethylene signaling in capsidiol elicitation in N. attenuata - A. alternata pathosystem. When NaEIN2 was silenced by VIGS, A. alternata -elicited NaF6’H1 was dramatically reduced, which is consistent with our previous finding that ethylene signaling is essential for scopoletin biosynthesis (Sun et al ., 2017), but NaEAH s and NaEAS s trancripts were induced to levels similar to plants transformed with empty vector (Supplementary Fig. S3).…”

“…Previously, we have demonstrated that, in response to A. alternata inoculation, N. attenuata plants activate both jasmonate and ethylene signaling pathways to regulate the biosynthesis of the phytoalexins scopoletin and its β-glycoside form, scopolin (Sun et al ., 2014b; Li and Wu, 2016; Sun et al ., 2017). As feruloyl-CoA 6’-hydroxylase 1 ( NaF6’H1 ), the key enzyme gene for scopoletin biosynthesis, was highly elicited at 1 day post inoculation (1 dpi) when the infection was at early stage and only a few of fungal hyphae had been observed to penetrate into leaf tissues via stomata (Sun et al ., 2014a), transcriptome analysis was performed in A. alternata -inoculated N. attenuata leaves at 1 dpi to identify secondary metabolites which could potentially act similarly to scopoletin.…”

“…The necrotrophic fungal pathogen Alternaria alternata (tobacco pathotype) causes brown spot disease in Nicotiana tabacum (LaMondia, 2001) and many other Nicotiana species, including the wild tobacco Nicotiana attenuata (Schuck et al ., 2014). Inoculation with A. alternata elicits the activation of both jasmonate and ethylene signaling pathways in N. attenuata plants, which subsequently lead to the accumulation of the phytoalexins, scopoletin and its glycoside form, scopolin (Sun et al ., 2014b; Li and Wu, 2016; Sun et al ., 2017). Currently it is not known if fungus-inoculated N. attenuata plants produce other phytoalexins, such as capsidiol.…”

NaPDR1 and NaPDR1-like are essential for the resistance of Nicotiana attenuata against fungal pathogen Alternaria alternata

“…To monitor the progress of VIGS, we silenced phytoene desaturase ( PDS ), which causes plants to show visible bleaching of green tissues two to three weeks after transformation ( Saedler and Baldwin, 2004 , Wu et al., 2008 , Sun et al., 2017 ). When the leaves of PDS -silenced plants began to bleach, the source–sink transition leaves of EV and VIGS plants were used for experiments.…”

“…Similar to cultivated tobacco, N. attenuata is attacked by A. alternata , a notorious necrotrophic fungus that causes brown spot disease in tobacco species in the field ( Schuck et al., 2014 ). In response to this fungal infection, N. attenuata plants activate abscisic acid (ABA)-mediated stomatal defense ( Sun et al., 2014a ), as well as the jasmonate (JA) and ethylene signaling pathways ( Sun et al., 2014b , Sun et al., 2017 , Li and Wu, 2016 ).…”