Expression of the Talaromyces flavus glucose oxidase gene in cotton and tobacco reduces fungal infection, but is also phytotoxic

Glucose oxidase secreted by the fungus Talaromyces flavus generates, in the presence of glucose, hydrogen peroxide that is toxic to phytopathogenic fu ngi responsible for economically important diseases in many crops. A glucos e oxidase gene from T. flavus, was modified with a carrot extensin signal p eptide and fused to either a constitutive or root-specific plant promoter. T-1 tobacco plants expressing the enzyme constitutively were protected agai nst infection by the seedling pathogen Rhizoctonia solani. Constitutive exp ression in tobacco was associated with reduced root growth, and slow germin ation on culture medium, and with reduced seed set in glasshouse conditions . Several independent transformed cotton plants with a root-specific constr uct expressed high glucose oxidase activity in the roots, excluding the roo t tip. Selected T-3 homozygous lines showed some protection against the roo t pathogen, Verticillium dahliae, but not against Fusarium oxysporum. High levels of glucose oxidase expression in cotton roots were associated with r educed height, seed set and seedling germination and reduced lateral root f ormation. If this gene is to be of value for crop protection against pathog ens it will require precise control of its expression to remove the deleter ious phenotypes.