Molecular Features Affecting the Biological Activity of the Host-Selective Toxins from Cochliobolus victoriae

Area of Science:

• Plant Pathology
• Biochemistry
• Molecular Biology

Background:

• Cochliobolus victoriae produces victorin toxins that affect susceptible oat varieties.
• The precise molecular mechanisms underlying victorin's phytotoxicity are not fully understood.

Purpose of the Study:

• To elucidate the structure-activity relationship of victorin toxins.
• To identify key chemical moieties responsible for victorin's inhibitory effects on CO2 fixation.

Main Methods:

• Synthesis and modification of victorin toxins (B, C, D, E) and victoricine.
• Assaying the effect of native and modified toxins on dark CO2 fixation in susceptible oat (Avena sativa) leaf slices.
• Quantifying half-maximal inhibitory concentrations (IC50) for various toxin derivatives.

Main Results:

• Native victorins inhibited dark CO2 fixation at micromolar concentrations (0.004–0.546 μM).
• The glyoxylic acid residue, specifically its hydrated aldehyde group, is essential for inhibitory activity.
• Removal of glyoxylic acid abolished inhibition; reduction of the aldehyde group conferred a protective effect.
• Esterification or beta-hydroxylysine derivatization significantly reduced inhibitory activity (to 10% and 1%, respectively), but host selectivity was retained.
• Macrocyclic ring opening drastically reduced inhibitory activity.

Conclusions:

• The glyoxylic acid moiety and its aldehyde group are critical for victorin's phytotoxic activity.
• Specific chemical modifications can attenuate or abolish victorin's inhibitory effects while potentially retaining host selectivity.
• Understanding these structure-activity relationships provides insights into victorin's mode of action and potential for developing resistant crop varieties.