Molecular responses of host tissue carbon metabolism to infection by powdery mildew (Erysiphe sp.)

Abstract

The powdery mildew fungi are biotrophic pathogens that form a complex interface, the haustorium, between the host plant and the parasite. The pathogen acts as an additional sink, competing with host sinks, such as flowers and roots, resulting in a considerable modification of photoassimilate production and partitioning within the host tissue.

This study investigated some of the factors that may contribute to these changes in the Arabidopsis thaliana / Erysiphe cichoracearum and wheat / Erysiphe graminis interactions. Glucose uptake into host tissues was enhanced following E. cichoracearum infection of Arabidopsis, showing inhibitor sensitivity consistent with that of a proton-coupled carrier mechanism mediating glucose uptake. This increased glucose uptake correlated with the induction of the monosaccharide transporter, AtSTP4 (Arabidopsis thaliana Sugar Transport Protein 4) in infected Arabidopsis leaves, shown by northern analysis and reverse transcriptase-polymerase chain reaction analysis (RT-PCR). Furthermore, prior to infection, Arabidopsis plants transformed with an AtSTP4 promoter-β-glucuronidase (GUS) construct showed expression only in sink tissues such as roots and flowers. Following infection, AtSTP4 expression is induced in the mature leaves and increases with time following infection. Sections of infected leaves stained for GUS showed that AtSTP4 expression is not confined to infected epidermal cells but is also evident in a wider range of cells, including those of the vascular tissue. In addition, RNase protection analysis also indicated that an AtSTP4 homologue was included in response to E. graminis infection of wheat.

The role of invertase following powdery mildew infection was also investigated.

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