Transcriptome analysis of quantitative resistance-specific response upon Ralstonia solanacearum infection in tomato.

Takeaki Ishihara,Hideki Takahashi,Ichiro Mitsuhara,Kazuhiro Nakaho,Zhengguang Zhang

doi:10.1371/journal.pone.0046763

Abstract

Bacterial wilt, caused by the soil-borne bacterium Ralstonia solanacearum, is a lethal disease of tomato, but the molecular mechanisms of the host resistance responses to R. solanacearum remain unclear. In this study, we report the first work describing the transcriptome of cultivar resistance and susceptible tomato cultivar after inoculation with R. solanacearum. To elucidate the characteristics of resistance early in the interaction, we analyzed microarrays for resistant cultivar LS-89 and susceptible cultivar Ponderosa 1 day after stem inoculation. No change in gene expression was detected for Ponderosa, but expression levels of over 140 genes, including pathogenesis-related, hormone signaling and lignin biosynthesis genes, increased in LS-89. Expression of β-1,3-glucanase genes increased substantially. In an immunohistochemical study, glucanase in LS-89 accumulated in the xylem and pith tissues surrounding xylem vessels filled with R. solanacearum. The expression of these genes also increased in four other resistant cultivars, but changed little in four susceptible cultivars in response to R. solanacearum, suggesting that similar reactions occur in other cultivars. These gene expression profiles will serve as fundamental information to elucidate the molecular mechanisms in the resistance response to R. solanacearum in tomato.

Highlights

Bacterial wilt caused by Ralstonia solanacearum is a major constraint in the production of solanaceous crops in tropical, subtropical and some warm temperate regions worldwide [1]
The gene expression profiles that we report here highlight some of the characteristics of quantitative resistance to R. solanacearum in LS-89 and may become powerful tools for elucidating the molecular mechanisms of resistance responses to R. solanacearum in tomato
We inoculated stems with a suspension of R. solanacearum (1.06106 colony forming units [CFU]/ml) just above the cotyledon of resistant cultivar LS-89, a popular commercial rootstock in Japan, and susceptible cultivar Ponderosa by cutting the stem to one-third of its diameter with a razor [22]

Summary

Introduction

Bacterial wilt caused by Ralstonia solanacearum is a major constraint in the production of solanaceous crops in tropical, subtropical and some warm temperate regions worldwide [1]. Cultivar resistance is the most effective means to control bacterial wilt in many crops, including tomato (Solanum lycopersicum) [1]. Tomato is one of the most important crops in the world, and numerous efforts to breed bacterial wilt-resistant cultivars have been undertaken for decades. In Japan and elsewhere, grafting of susceptible but high-quality tomato cultivars onto resistant rootstock cultivars has been widely adopted to manage bacterial wilt [2]. Major sources of bacterial wilt resistance in cultivated tomato are wild tomatoes S. pimpinellifolium and S. lycopersicum var. Even though a resistance response is induced in both roots and stems, resistance to bacterial wilt is not associated with inhibition of bacterial root invasion but with the ability of the plant to limit bacterial colonization in the stem; the degree of disease resistance is related to the extent that

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Conclusion