FUNCTIONAL GENOMICS OF AGRONOMIC TRAITS IN DEVELOPING SEED AND POLLEN IN MAIZE AND SORGHUM
Location: Chemistry Research Unit
Title: Pleiotropy and its limited dissection through a metabolic gene Miniature1 (Mn1) that encodes a cell wall invertase in developing seeds of maize.
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2011
Publication Date: December 14, 2011
Citation: Chourey, P.S., Li, Q., Cevallos-Cevallos, J. 2011. Pleiotropy and its limited dissection through a metabolic gene Miniature1 (Mn1) that encodes a cell wall invertase in developing seeds of maize. Plant Science. 184:45-53.
Interpretive Summary: Pleiotropy refers to a control of multiple traits by a single gene; how this is manifested and its functional meaning remains a major challenge in Genetics. In this study, we are focused on Miniature (Mn1) gene in maize that codes for a seed-specific cell wall invertase. The loss of this enzyme due to a mutation at the Mn1 locus leads to ~ 70% loss of seed weight and several diverse changes (pleiotropic) in a developing seed. A cooperative investigation between scientists from CMAVE, USDA ARS, and the University of Florida, at Gainesville, FL, provide data showing (1) that the mn1 mutation leads to simultaneous loss of mass (weight) in two distinctive domains of a developing seed, endosperm - source of food, feed and fuel, and embryo (germ); and (2) changes in the expression of many endosperm genes in metabolic pathways relating to sugar utilization that are essential to normal seed development. Such molecular dissection allows identification and subsequent characterization of interacting genes and proteins that may contribute to sink size, seed mass and, ultimately, greater crop productivity.
The Mn1-encoded endosperm-specific cell wall invertase is a major determinant of sink strength of developing seeds through its control of both sink size, cell number and cell size, and sink activity via sucrose hydrolysis and release of hexoses essential for energy and signaling functions. Consequently, loss-of-function mutations of the gene lead to the mn1 seed phenotype that shows ~ 70% reduction in seed mass at maturity and several pleiotropic changes. Through a comparative analysis of endosperm and embryo mass in the Mn1 and mn1 genotypes we observed here significant reductions of both tissues in the mn1 starting with early stages of development. Clearly, embryo development was endosperm-dependent. To gain a mechanistic understanding of the changes, sugar levels were measured in both endosperm and embryo samples. Levels of all sugars tested, glc, fru, suc, and sorbitol, were altered in both endosperm and embryo. Greatly reduced fru levels in the mutant led to RNA level expression analyses by q-PCR of several genes that encode sucrose and fructose metabolizing enzymes. Variable levels of reduction in gene expression, ranging from 0.5% to ~30% of the Mn1 samples, was seen in the mn1 for both suc – starch and suc - energy pathways, suggesting an in vivo metabolic coordinated reduction due to the hexose-deficiency. Together, these data provide evidence of the Mn1-dependent interconnected network of several pathways as a possible basis for pleiotropic changes in seed development.