Increased Expression of the Tomato SISWEET15 Gene During Grey Mold Infection and the Possible Involvement of the Sugar Efflux to Apoplasm in the Disease Susceptibility

Yuichiro Asai,Yuhko Kobayashi

doi:10.4172/2157-7471.1000329

Abstract

Host plant susceptibility genes, which facilitate pathogen growth during plant infection, are attractive targets for disease-resistance breeding. To explore candidate susceptibility genes in tomatoes during Botrytis cinerea infection, the fungal infection-responsive SWEET genes were screened for out of all 31 tomato SlSWEET genes. The expression of only one gene, SlSWEET15, was induced by B. cinerea at the pre-necrotic stage (16 h post inoculation), whereas most of the other SWEET genes were downregulated. The expression of the SlSWEET15 transiently increased by 16 h post inoculation, then reduced to basal levels by 24 h post inoculation. We measured the glucose and sucrose contents of fluid of infected cotyledons at the pre-necrotic stage (20 h post inoculation). The sugar contents of the apoplasmic fluids were significantly higher in the infected cotyledons compared to 0 h. Furthermore, glucose and sucrose can promote growth and invasion of B. cinerea both in vitro and in vivo. SWEET proteins in clade III, including the deduced SlSWEET15, are well-known sugar efflux transporters. These results suggest that SlSWEET15 is induced by B. cinerea and that this is exploited by the fungus, which may provide sugars to promote hyphal growth in the pre-necrotic stage of infection in tomato.

Highlights

Necrotrophic fungi are the largest class of fungal phytopathogens and cause serious crop losses worldwide [1]
Primer sets for all 31 tomato SWEET (SlSWEET) genes were designed, and the expression of each gene was investigated by quantitative reverse transcription PCR (qRT-PCR) at 0 h and 16 h post inoculation with B. cinerea
The changes in gene expression of the 31 sets for all tomato SWEET (SlSWEET) at an early stage of B. cinerea infection were investigated by qRT-PCR (Figure 1)

Summary

Introduction

Necrotrophic fungi are the largest class of fungal phytopathogens and cause serious crop losses worldwide [1]. A typical necrotrophic fungus, is an important plant pathogen with a wide range of host plants, causing gray mold disease in over 200 plant species, including most vegetable and fruit crops, trees and flowers [2]. B. cinerea causes massive losses in some field and greenhouse-grown horticultural crops, including tomatoes [3]. The damage to tomato yields caused by B. cinerea is enormous, and the fungus is difficult to control because it has a variety of pathogenic mechanisms, that can use diverse hosts as inoculum sources, and can survive as mycelia and/or conidia or for extended periods as sclerotia in crop debris [3]. Powdery mildew resistant gene mlo was originally discovered in barley and characterized as a membrane-anchored protein [6]. MLO seems to be required for susceptibility to adapted pathogens, and mlo mutants display a loss of susceptibility resembling that described for non-host resistance [7]

Methods

Results

Conclusion