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Using Ustilago maydis as a Trojan Horse for In Situ Delivery of Maize Proteins
Published on: February 8, 2019
The binding of host-selective toxin analogs to mitochondria from normal and ;texas' male sterile cytoplasm maize
K A Frantzen1, J M Daly, H W Knoche
1Department of Agricultural Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska.
Abstract:
Tritium-labeled toxin analogs were prepared by reduction with NaB(3)H(4) of either the toxin from Helminthosporium maydis race T or a toxin component from Phyllosticta maydis. These reduced analogs had high radiochemical specific activities, high biological activities, and plant specificities identical to the native toxins. A filtration assay was developed to test the binding of these labeled analogs to isolated mitochondria. Binding was not energy dependent nor was there measurable matrical uptake. The analogs were shown to be lipophilic, a characteristic which gave rise to considerable nondisplaceable binding. Under conditions limiting nondisplaceable binding, the displaceable binding was shown to be linear with respect to toxin concentration and unsaturable. No significant differences were observed in the binding characteristics between the mitochondria from normal and male-sterile (Texas) cytoplasm maize. The findings suggest that, at physiologically relevant concentrations, these toxin analogs permeate the membranes of susceptible and resistant mitochondria alike. The lack of demonstrable specific binding does not rule out the involvement of a classical receptor site but does indicate that other kinds of molecular interactions may be involved in the mechanisms for toxicity and specificity.
Insights
Toxin analogs from Helminthosporium maydis race T and Phyllosticta maydis were labeled with tritium. These analogs permeated maize mitochondria membranes, suggesting non-receptor interactions in toxin activity.
Area of Science:
- Biochemistry
- Plant Pathology
- Molecular Biology
Background:
- Helminthosporium maydis race T and Phyllosticta maydis toxins affect maize.
- Understanding toxin-host interactions is crucial for crop protection.
Purpose of the Study:
- To synthesize and characterize tritium-labeled toxin analogs.
- To investigate the binding of these analogs to maize mitochondria.
Main Methods:
- Preparation of tritium-labeled toxin analogs via NaB(3)H(4) reduction.
- Filtration assay to assess analog binding to isolated mitochondria.
- Analysis of binding characteristics (energy dependence, uptake, lipophilicity, saturation).
Main Results:
- Synthesized analogs exhibited high radiochemical and biological activity, identical to native toxins.
- Binding was not energy-dependent and showed no measurable matrix uptake.
- Analogs demonstrated lipophilic properties leading to significant nondisplaceable binding.
- Displaceable binding was linear with concentration and unsaturable.
- No significant differences in binding were observed between normal and male-sterile (Texas) cytoplasm maize mitochondria.
Conclusions:
- Toxin analogs permeate maize mitochondria membranes at physiological concentrations.
- Lack of specific binding suggests potential non-classical receptor interactions in toxin mechanisms.
- Findings contribute to understanding maize-mitochondria toxin interactions and specificity.
