|Carillo Vazquez, Gricelda|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2006
Publication Date: 11/29/2006
Citation: Jia, H., Nettleton, D., Carillo Vazquez, G., Peterson, J., Scott, M.P. 2006. Comparison of transcript profiles in wild-type and 02 maize endosperm in different genetic backgrounds. Crop Sci. (The Plant Genome). 47:S-45-59. Interpretive Summary: Maize grain is one of the most important ingredients of livestock and poultry diets in the U.S. Expensive supplements must be added to these diets to meet the dietary requirements of these animals. Thus, maize with higher content of essential nutrients benefits consumers because it reduces the cost of animal feed, thereby reducing the cost of meat production. Maize carrying the opaque 2 mutation has increased levels of essential amino acids, which are limiting nutrients in animal feed. Unfortunately, this maize has many agronomic problems that make it unsuitable to commercial use. Better understanding of opaque 2 function may allow us to develop maize with improved nutritional quality as well as good agronomic characteristics. In order to understand how the opaque2 gene functions, we identified genes that were expressed differently in opaque 2 lines than in their wild-type counterparts. By examining several inbred line pairs in this way, we have learned how the genetic background influences the effects of the opaque 2 mutation. We also identified a minimal set of genes that we consider to be "main effect" genes, rather than "genotype specific" genes. Scientists working with opaque2 can focus on these genes which are likely to be involved in controlling effects of opaque2. This work will allow scientists to develop corn with improved nutritional quality and agronomic peformance. Ultimately, this will benefit consumers by reducing the cost of food production.
Technical Abstract: Mutations in the Opaque2 (O2) gene of maize (Zea mays L.) improve the nutritional value of maize by reducing the level of zeins in the kernel. The phenotype of o2 grain is controlled by many modifier genes and is, therefore, strongly dependent on genetic background. We propose two hypotheses to explain differences in phenotypic severity in different genetic backgrounds: 1) specific genes are differentially (o2 vs wild-type) expressed only in certain genotypes and 2) the same genes are differentially expressed in all backgrounds, but the degree of differential expression differs in different backgrounds. Eight pairs of inbred lines and their o2 counterparts were characterized for phenotypes influenced by o2 (lysine content, kernel density, seed weight and shoot:root ratio of seedlings). The inbred line B46 was identified as having severe o2 phenotypes while the line M14 was identified as having minimal o2 phenotypes. Transcripts that were differentially expressed between the wild-type and o2 versions of these two lines were identified by microarray hybridization. While some genotype-specific differentially expressed transcripts were identified, many transcripts were identified having reduced degree of differential expression in M14 relative to B46. Thus, a combination of genotype-specific differential expression and degree of differential expression of transcripts can explain differences in phenotypic severity between M14 and B46. To identify transcripts likely to be differentially expressed in a given genetic background, we averaged out genotype-specific effects by comparing transcript levels in pools of RNA from eight o2 genotypes with transcript levels in the eight corresponding wild-type genotypes.