Start Date: Oct 19, 2010
End Date: Mar 25, 2013
Objective 1: Soybean oil synthesis and deposition occur mainly in cotyledons and are differentially regulated over the course of seed maturation. The oil synthesis and deposition are accomplished through the concerted activities of many gene products and biological pathways that are primarily regulated at transcription levels. Gene expression patterns change very quickly over the course of an organism’s evolution if it is not subjected to functional constraints. Although it is not a universal rule, evidence suggests that expression patterns of many genes are intended to co-evolve with their biological functionalities. The co-evolution is reflected by a correlation of gene expression pattern with the related biological functions, and co-expression of functionally related genes such as those that encode proteins that reside in the same metabolic or signal pathways, or in the same cellular complexes under a variety of biological conditions (Stuart et al., 2003; Wei et al., 2006). The expression pattern correlation is widely used as criteria to predict biological functions of genes, functional relatedness between genes, and gene regulatory networks (Horan et al., 2008). We have examined transcriptomes and storage lipid profiles of cotyledons at six distinct developmental stages over the course of seed maturation. Objective 2: We have conducted deep sequencing of small RNA populations in the same RNA preparations used for transcriptome analysis. It is believed that miRNAs function as master regulators in gene regulatory networks underlying diverse biological processes in Arabidopsis. However, much less is known about soybean miRNA species and their accumulation patterns over the course of seed maturation. As part of our effort to delineate regulatory networks and identify key genetic components controlling oil composition and content, we will conduct genome-wide characterization of small RNAs, particularly miRNAs, in cotyledons over the course of seed maturation. We will use a bioinformatic approach to analyze the small RNA sequences we have conducted to discover miRNA species and their accumulation patterns. MiRNA species recognize their target mRNA by high sequence complementation, and function mainly as suppressors of the accumulation of the target mRNA by directing the degradation of its functional target mRNAs in plants. Sequence complementarities and negative correlation of mRNA and miRNA accumulation patterns should offer a more effective approach to identify the functional target genes, and can be used to delineate the topology of small RNAs in the TF networks inferred in Objective 1. The miRNA species that locate in TF networks enriched with oil related genes or target oil related genes would be strong candidates for future investigations for oil composition and content improvement.