Temporal and Spatial Resolution of Activated Plant Defense Responses in Leaves of Nicotiana benthamiana Infected with Dickeya dadantii.

María L Pérez-Bueno,Mónica Pineda,Matilde Barón,Emilia López-Solanilla,Espen Granum,Pablo Rodriguez-Palenzuela,Víctor Flors

doi:10.3389/fpls.2015.01209

Abstract

The necrotrophic bacteria Dickeya dadantii is the causal agent of soft-rot disease in a broad range of hosts. The model plant Nicotiana benthamiana, commonly used as experimental host for a very broad range of plant pathogens, is susceptible to infection by D. dadantii. The inoculation with D. dadantii at high dose seems to overcome the plant defense capacity, inducing maceration and death of the tissue, although restricted to the infiltrated area. By contrast, the output of the defense response to low dose inoculation is inhibition of maceration and limitation in the growth, or even eradication, of bacteria. Responses of tissue invaded by bacteria (neighboring the infiltrated areas after 2–3 days post-inoculation) included: (i) inhibition of photosynthesis in terms of photosystem II efficiency; (ii) activation of energy dissipation as non-photochemical quenching in photosystem II, which is related to the activation of plant defense mechanisms; and (iii) accumulation of secondary metabolites in cell walls of the epidermis (lignins) and the apoplast of the mesophyll (phytoalexins). Infiltrated tissues showed an increase in the content of the main hormones regulating stress responses, including abscisic acid, jasmonic acid, and salicylic acid. We propose a mechanism involving the three hormones by which N. benthamiana could activate an efficient defense response against D. dadantii.

Highlights

The necrotrophic bacteria Dickeya sp. and Pectobacterium sp. are the causal agents of the soft-rot disease in a broad range of hosts, affecting one-half of angiosperm plant orders (Ma et al, 2007)
In previous studies on Nicotiana benthamiana plants infected with pepper mild mottle virus (Pérez-Bueno et al, 2006) as well as on Phaseolus vulgaris infected with Pseudomonas syringae pv. phaseolicola (Rodríguez-Moreno et al, 2008; Pérez-Bueno et al, 2015), we demonstrated that NPQ plays an important role in plant defense against pathogens
The response of N. benthamiana to bacterial challenge was analyzed by comparing the effects of inoculation using two bacterial concentrations: the so called LD (104 cfu ml−1), considered to be closer to natural infection conditions, and HD (106 cfu ml−1)

Summary

Introduction

The necrotrophic bacteria Dickeya sp. and Pectobacterium sp. are the causal agents of the soft-rot disease in a broad range of hosts, affecting one-half of angiosperm plant orders (Ma et al, 2007). Are the causal agents of the soft-rot disease in a broad range of hosts, affecting one-half of angiosperm plant orders (Ma et al, 2007). As a result, they cause great economic losses in crops and ornamental plants world-wide (Reverchon and Nasser, 2013). N. benthamiana Responses against D. dadantii was originally isolated from African violet (Saintpaulia ionantha). This necrotrophic bacterium is especially pernicious due to its ability to cause latent infections, which become active in post-harvest, affecting the shelf life of the product. In Southern Europe, D. dadantii has been identified as an emergent problem (Palacio-Bielsa et al, 2010)

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