Submitted to: Journal of Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/21/2011
Publication Date: 5/10/2011
Citation: Johnson, E.T., Dowd, P.F., Liu, Z., Musser, R.O. 2011. Comparative transcription profiling analyses of maize reveals candidate defensive genes for seedling resistance against corn earworm. Molecular Genetics and Genomics. 285(6):517-525. Interpretive Summary: Insect damage to crops causes significant economic losses each year. Insect damage can cause fungal contamination which also leads to losses. New sources of insect and fungal resistance, preferably identified from plant sources, would minimize these losses. Young corn plants germinating through the soil face a number of potential pathogens and insects before fully developing. Using current gene technology (microarrays), we have identified a number of genes being expressed in young corn seedlings that possibly contribute to resisting pathogens and insects. Our results indicate that the seedlings utilize a wide variety of resistance mechanisms to protect themselves from harm. Many of the genes we identified correlated to genes identified in earlier studies that documented a role in pathogen or insect resistance. These findings will now allow us to begin engineering novel resistance mechanisms that will be expressed in mature tissues as well. Corn with enhanced levels of insect and pathogen resistance will result in higher yields and low levels of toxins produced by fungi (mycotoxins) that is safe for human and livestock consumption.
Technical Abstract: As maize seedlings germinate into the soil, they encounter an environment teaming 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. Bioassays indicated maize seedlings were more toxic to caterpillars than shoots from 3 or 4 leafed plants. Microarray technology 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-dihyrdoxy-7-methoxy-1,4-benzoxazin-3-one), an anti-insect resistance molecule, other highly expressed genes in the seedling encode the following putative proteins: defensin, hydroxyproline and proline-rich protein, thaumatin-like protein, lipase, cystatin, protease-inhibitor, and a variety of proteases. Changes in the levels of gene expression by the microarray technology were well correlated to results using quantitative RT-PCR. The potential resistance genes identified ocurred mainly on chromosomes 1 and 5 in the B73 genome. Analysis of promoters of four DIMBOA biosynthetic genes determined that a Dof transcription factor, two of which were differently expressed in three vegetative stages, is 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.