Drought Stress Acclimation Imparts Tolerance to Sclerotinia sclerotiorum and Pseudomonas syringae in Nicotiana benthamiana

Abstract

Acclimation of plants with an abiotic stress can impart tolerance to some biotic stresses. Such a priming response has not been widely studied. In particular, little is known about enhanced defense capacity of drought stress acclimated plants to fungal and bacterial pathogens. Here we show that prior drought acclimation in Nicotiana benthamiana plants imparts tolerance to necrotrophic fungus, Sclerotinia sclerotiorum, and also to hemi-biotrophic bacterial pathogen, Pseudomonas syringae pv. tabaci. S. sclerotiorum inoculation on N. benthamiana plants acclimated with drought stress lead to less disease-induced cell death compared to non-acclimated plants. Furthermore, inoculation of P. syringae pv. tabaci on N. benthamiana plants acclimated to moderate drought stress showed reduced disease symptoms. The levels of reactive oxygen species (ROS) in drought acclimated plants were highly correlated with disease resistance. Further, in planta growth of GFPuv expressing P. syringae pv. tabaci on plants pre-treated with methyl viologen showed complete inhibition of bacterial growth. Taken together, these experimental results suggested a role for ROS generated during drought acclimation in imparting tolerance against S. sclerotiorum and P. syringae pv. tabaci. We speculate that the generation of ROS during drought acclimation primed a defense response in plants that subsequently caused the tolerance against the pathogens tested.

Impact of Concurrent Drought Stress and Pathogen Infection on Plants

“…tabaci (causal agent of wildfire disease in tobacco) (Ramegowda et al 2013). The degree of disease tolerance in droughtstressed plants was correlated to the extent of reactive oxygen species (ROS) accumulation (Ramegowda et al 2013). The relation of increased ROS content to defense against bacterial infection was further substantiated by the application of methyl viologen (MV), a compound that provokes ROS production by disrupting electron transport chain in chloroplast.…”

“…For example, drought stress has been shown to aggravate many fungal (Mayek-Perez et al 2002), bacterial (McElrone et al 2001Mohr and Cahill 2003), and viral (Olson et al 1990;Prasch and Sonnewald 2013) infections in plants. On the contrary, in the second case, the drought stress has been shown to enhance the tolerance of the plants toward pathogens (Ramegowda et al 2013;Achuo et al 2006). The nature and outcome of plant-pathogen interaction under drought stress differs with the type of pathogens (fungi, oomycete, bacteria, and viruses) as they employ different strategies for infection.…”

“…The acclimation of N. benthamiana plants to moderate drought stress (40-60 % field capacity [FC] of soil) increased its tolerance to bacterial pathogen P. syringae pv. tabaci (causal agent of wildfire disease in tobacco) (Ramegowda et al 2013). The degree of disease tolerance in droughtstressed plants was correlated to the extent of reactive oxygen species (ROS) accumulation (Ramegowda et al 2013).…”

“…The relation of increased ROS content to defense against bacterial infection was further substantiated by the application of methyl viologen (MV), a compound that provokes ROS production by disrupting electron transport chain in chloroplast. The MV-treated plants had high ROS and showed decreased bacterial growth (Ramegowda et al 2013). Drought stress can also help prevent pathogen multiplication and spread.…”

“…Ramegowda et al (2013) showed that upon infection with Sclerotinia sclerotiorum (causal agent of white mold in beans), the well-watered Nicotiana benthamiana plants showed severe cell death, whereas the droughtacclimated plants exhibited reduced cell death. Thus, moderate drought was found to enhance plant's defense against pathogens by inducing expression of defense-related genes.…”