RNA-seq analysis and fluorescence imaging of melon powdery mildew disease reveal an orchestrated reprogramming of host physiology

Álvaro Polonio,Rocío Bautista,Jesús Martínez-Cruz,Mónica Pineda,Matilde Barón,María Luisa Pérez-Bueno,Alejandro Pérez-García

doi:10.1038/s41598-019-44443-5

Abstract

The cucurbit powdery mildew elicited by Podosphaera xanthii is one of the most important limiting factors in cucurbit production. Our knowledge of the genetic and molecular bases underlying the physiological processes governing this disease is very limited. We used RNA-sequencing to identify differentially expressed genes in leaves of Cucumis melo upon inoculation with P. xanthii, using RNA samples obtained at different time points during the early stages of infection and their corresponding uninfected controls. In parallel, melon plants were phenotypically characterized using imaging techniques. We found a high number of differentially expressed genes (DEGs) in infected plants, which allowed for the identification of many plant processes that were dysregulated by the infection. Among those, genes involved in photosynthesis and related processes were found to be upregulated, whereas genes involved in secondary metabolism pathways, such as phenylpropanoid biosynthesis, were downregulated. These changes in gene expression could be functionally validated by chlorophyll fluorescence imaging and blue-green fluorescence imaging analyses, which corroborated the alterations in photosynthetic activity and the suppression of phenolic compound biosynthesis. The powdery mildew disease in melon is a consequence of a complex and multifaceted process that involves the dysregulation of many plant pathways such as primary and secondary metabolism.

Highlights

The Cucurbitaceae or cucurbit family includes many economically important species, those with edible fruits such as cucumber, melon, watermelon, zucchini and pumpkin[1]
Different imaging techniques are currently widely used in plant physiology to assess the impact of biotic stress on host plants since they reveal the metabolic gradients that pathogens usually induce in infected leaves[29,30]
The so-called blue-green fluorescence (BGF) is a valuable technique to study secondary metabolism, since phenolic compounds from the phenylpropanoid pathway are the primary emitters of that fluorescence[33,34]

Summary

Introduction

The Cucurbitaceae or cucurbit family includes many economically important species, those with edible fruits such as cucumber, melon, watermelon, zucchini and pumpkin[1]. An understanding of disease mechanisms at the molecular level is of paramount importance for identifying possible intervention points for their control[22] For this reason, several studies have used RNA-seq analysis to obtain a more comprehensive view of the primary molecular mechanisms that are dysregulated in plants upon pathogen inoculation[23,24,25,26,27]. Whole-transcriptome changes during early disease stages in susceptible plant species are less well-documented than those of resistant ones This is the case for cucurbit-powdery mildew interactions. Different imaging techniques are currently widely used in plant physiology to assess the impact of biotic stress on host plants since they reveal the metabolic gradients that pathogens usually induce in infected leaves[29,30] Examples of these techniques include chlorophyll fluorescence imaging (Chl-FI) and multicolour fluorescence imaging (MCFI). Many plant-pathogen interactions have been subject to analysis using imaging techniques[29,35] and most of them have the primary aim of identifying specific disease identity marks

Methods

Results

Conclusion