Differential expression of genes during legume seed development

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Abstract
The accumulation of certain proteins specific to those tissues in the developing seeds of legumes represents a system of academic and practical significance in the study of differential gene expression. Besides the simple distinction between ‘seed-specific’ and ‘non-seed-specific’ expression of genes, further controls are present in determining the level of expression of a particular gene, and the variations in its expression with cell type, developmental stage and environmental perturbation. There are also genetic factors that lead to variations in the expression of homologous genes between lines or species. Gene expression can be assayed at the levels of synthesis of specific proteins, level of mRNA species, and transcription of specific genes, and the results of all these assays lead to a broad correlation between events at the level of the gene and protein deposition in the developing seed. This correlation is strong at earlier stages of seed development, but is weaker at later stages. Evidence is presented that control of gene expression occurs both at transcription and by post-transcriptional processes. Seed protein genes have conserved sequences in their 5' flanking regions that are specific to gene families, and these are suggested to be involved in transcriptional control of the expression of these genes. Although such sequences are unlikely to be solely responsible for transcription control, there is no strong evidence for changes in DNA methylation or in chromatin conformation being causally related to expression of seed protein genes. Control of gene expression in developing seeds is considered in terms of a genetically determined, conserved developmental programme, the aim of which is to produce a viable embryo. This programme will allow considerable plasticity in gene expression within constraints prescribed by seed viability. Although it may be possible to understand the immediate controls of seed protein gene expression, present systems are not adequate to study the genes that control the developmental programme. More fundamental investigations will be assisted by mutants that possess altered seed development patterns.