Comparative transcription profiling analyses of maize reveals candidate defensive genes for seedling resistance against corn earworm.

As maize seedlings germinate into the soil, they encounter an environment teeming with insects seeking rich sources of nutrition. Maize presumably has developed a number of molecular mechanisms to ensure survival at the beginning of its life cycle. Comparative transcription analysis using microarrays was utilized to document the expression of a number of genes with potential defensive functions in seedling tissue. In addition to elevated levels of the genes involved in the biosynthesis of DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), an anti-insect resistance molecule, other highly expressed genes in the seedling encode the following putative defensive proteins: defensin, hydroxyproline and proline-rich protein, thaumatin-like protein, lipase, cystatin, protease inhibitor, and a variety of proteases. The potential resistance genes identified occurred mainly on chromosomes 1 and 5 in the B73 genome. Analysis of promoters of seven DIMBOA biosynthetic genes identified three transcription factor binding sites that are possibly involved in regulation of the DIMBOA biosynthetic pathway. The results indicate that maize employs a wide variety of potential resistance mechanisms in seedling tissue to resist a possible insect attack.