Abstract
BackgroundPlant sucrose transporter activities were shown to respond to changes in the extracellular pH and redox status, and oxidizing compounds like glutathione (GSSG) or H2O2 were reported to effect the subcellular targeting of these proteins. We hypothesized that changes in both parameters might be used to modulate the activities of competing sucrose transporters at a plant/pathogen interface. We, therefore, compared the effects of redox-active compounds and of extracellular pH on the sucrose transporters UmSRT1 and ZmSUT1 known to compete for extracellular sucrose in the Ustilago maydis (corn smut)/Zea mays (maize) pathosystem.Methodology/Principal FindingsWe present functional analyses of the U. maydis sucrose transporter UmSRT1 and of the plant sucrose transporters ZmSUT1 and StSUT1 in Saccharomyces cerevisiae or in Xenopus laevis oocytes in the presence of different extracellular pH-values and redox systems, and study the possible effects of these treatments on the subcellular targeting. We observed an inverse regulation of host and pathogen sucrose transporters by changes in the apoplastic pH. Under none of the conditions analyzed, we could confirm the reported effects of redox-active compounds.Conclusions/SignificanceOur data suggest that changes in the extracellular pH but not of the extracellular redox status might be used to oppositely adjust the transport activities of plant and fungal sucrose transporters at the host/pathogen interface.
Highlights
Recently, UmSRT1, the first fungal sucrose transporter, was identified in the plasma membrane of the maize (Zea mays) pathogen Ustilago maydis
At later stages of development, U. maydis hyphae typically grow along the phloem of infected maize plants, where they have access to sucrose released from this long-distance transport tissue [1]
We studied the effect of the reducing compound GSH (Fig. 8C, 8D and 8F) or of the oxidizing compounds GSSG (Fig. 8E) and H2O2 (Fig. 8G and 8H) on the distribution of GFP-labeled UmSRT1 protein within the plasma membrane of UmSRT1-GFPexpressing yeast cells
Summary
UmSRT1, the first fungal sucrose transporter, was identified in the plasma membrane of the maize (Zea mays) pathogen Ustilago maydis (corn smut [1]). Deletion of the UmSRT1 gene results in an almost complete loss of symptom development and tumor formation This demonstrated that UmSRT1 is essential for the virulence of U. maydis [1]. The biotrophic basidiomycete U. maydis occurs ubiquitously and depends on living plant material for growth and propagation. As it does not use aggressive virulence strategies it can persist for long periods on its live host without causing induction of apparent defense responses [3,4]. We compared the effects of redox-active compounds and of extracellular pH on the sucrose transporters UmSRT1 and ZmSUT1 known to compete for extracellular sucrose in the Ustilago maydis (corn smut)/Zea mays (maize) pathosystem
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