Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans.

Dharani Dhar Burra,Erland Liljeroth,Erik Andreasson,Jenny Morris,Fredrik Levander,Svante Resjö,Pete E Hedley,Erik Alexandersson,Oliver Berkowitz

doi:10.1186/s12870-014-0254-y

Abstract

BackgroundPotato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss. We investigated the transcriptome of Solanum tubersoum (cv. Desiree) and characterized the secretome by quantitative proteomics after foliar application of the protective agent phosphite. We also studied the distribution of phosphite in planta after application and tested transgenic potato lines with impaired in salicylic and jasmonic acid signaling.ResultsPhosphite had a rapid and transient effect on the transcriptome, with a clear response 3 h after treatment. Strikingly this effect lasted less than 24 h, whereas protection was observed throughout all time points tested. In contrast, 67 secretome proteins predominantly associated with cell-wall processes and defense changed in abundance at 48 h after treatment. Transcripts associated with defense, wounding, and oxidative stress constituted the core of the phosphite response. We also observed changes in primary metabolism and cell wall-related processes. These changes were shown not to be due to phosphate depletion or acidification caused by phosphite treatment. Of the phosphite-regulated transcripts 40% also changed with β-aminobutyric acid (BABA) as an elicitor, while the defence gene PR1 was only up-regulated by BABA. Although phosphite was shown to be distributed in planta to parts not directly exposed to phosphite, no protection in leaves without direct foliar application was observed. Furthermore, the analysis of transgenic potato lines indicated that the phosphite-mediated resistance was independent of the plant hormones salicylic and jasmonic acid.ConclusionsOur study suggests that a rapid phosphite-triggered response is important to confer long-lasting resistance against P. infestans and gives molecular understanding of its successful field applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0254-y) contains supplementary material, which is available to authorized users.

Highlights

Potato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss
Phosphite-induced protection against P. infestans is observed in detached leaflet assay throughout the time series A clear reduction of P. infestans infection was observed at all tested time points after phosphite treatment, i.e. 3, 6, 11, 24 and 120 h (Figure 1)
The phosphite treated leaflets showed “HR-like” (“hypersensitive response like”) symptoms at the site of P. infestans inoculation compared to extensive sporulation observed on control leaflets 7 days after infection (Additional file 1: Figure S1A)

Summary

Introduction

Potato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss. Potato late blight disease caused by the oomycete pathogen Phytophthora infestans is among the most severely damaging diseases of the potato crop. BABA has been shown to induce salicylic acid (SA)-dependent induced resistance against P. infestans in potato [8,9]. Metabolically inert phosphite-based compounds that have a direct inhibitory effect on the mycelial growth of P. infestans [10,11,12,13] have been shown to induce resistance in potato against late blight disease [14,15,16]. Phosphite-based compounds are marketed as fertilizers, activators of natural resistance or systemic fungicides and are widely used in some developing countries where they because of the low risk to human health and environment have been identified as potential alternatives to conventional fungicides [17]

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Conclusion