Identification and properties of insect resistance-associated maize anionic peroxidases

Previous studies with transgenic plants have indicated a tobacco anionic peroxidase can confer enhanced resistance to a variety of insects when expressed in different plant species. Tissue that expresses high levels of this enzyme often browns rapidly when damaged. Maize roots damaged under sterile conditions browned and had an anionic peroxidase induced. When introduced biolistically, maize callus transformants expressing a maize peroxidase gene with a predicted isoelectric point of ca. 5.1 produced browner callus compared to a corresponding beta-glucuronidase (GUS) transformant as callus aged. Higher production of only one isozyme of ca. pI 4.5 was noted. When the callus was fed to two maize pest caterpillar species, growth rates were slower (as reflected by weights) relative to the GUS callus. Based on examination of published information and electrophoretic properties, this gene appears to code for Px11, a peroxidase isozyme that is primarily produced in root tissue and callus. When sequence of the gene in several inbreds was examined, coding variations were noted, and abilities to utilize ferulic and p-coumaric acids differed. These coding differences may influence the ability of corresponding forms of the peroxidase to promote resistance. In addition to potential use in marker assisted breeding, enhanced expression of this anionic peroxidase through breeding or genetic engineering may lead to enhanced insect or disease resistance.