Seed development in peas: knowing your three ‘r's’ (or four, or five)

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Abstract
The value of the garden pea (Pisum sativum) both as an experimental tool and food crop has led to an accumulated wealth of genetic variation. This paper describes how some of the variation may be harnessed for studying seed development. One can identify genotypic differences for maternal, embryonic and cellular components and the interaction between them. The impact of these components on processes such as cell division, partitioning and the deposition of storage products can then be assessed by utilizing new techniques such as immunocytochemistry and in situ hybridization.The rugosus loci, which induce wrinkling of the seed, are examples of how major genes can be exploited to dissect seed development. Alleles at one of these loci, r, have been defined at both the molecular and biochemical levels. A much clearer picture can now be drawn of the pleiotropic nature of the genes, from their effects on starch composition to those on cellular development, which has implications for seed development in many species. The rugosus loci are the only ones known to affect seed development in peas. By analogy with cereal seeds, however, one would anticipate other mutants in the starch pathway which also affect the shape of the seed. Here, we report the induction of new rugosus-like mutants, compare them to starch mutants in other species and examine the ways in which they may help our understanding of starch biosynthesis and the regulation of seed development.