Evol Ecol Res 12: 855-871 (2010) Full PDF if your library subscribes.
Evolution of exalbuminous seeds as a result of competition between maternally derived and paternally derived genes
Department of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Aoba, Japan
Correspondence: S. Sakai, Department of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980–8578, Japan.
Background: The endosperm of angiosperm seeds absorbs resources from the female parent to support the embryo. The endosperm has three nuclei; two are maternally derived (madumnal) and one is paternally derived (padumnal). Some species have albuminous seeds; that is, at seed maturity, the endosperm contains most of the seed’s stored resources and the embryo is small. Other species have exalbuminous seeds; that is, before seed maturity, the cotyledons absorb most or all the endosperm and the embryo is relatively large. There are two sorts of exalbuminous seeds: (1) The cotyledons of some species absorb most of the endosperm towards the end of maturation. Their genes regulate the absorption process but the embryo does not directly absorb resources from the female parent. (2) The cotyledons of other species completely absorb the endosperm very early in seed maturation, and then absorb resources from the female parent directly. In such species, genes expressed in cotyledons communicate with parental tissues regarding demand for resources.
Question: How might natural selection account for the differences in exalbuminous seed development?
Method: Analysis of evolutionarily stable strategy (ESS) using a game-theoretic model of seed production.
Key assumptions: Madumnal and padumnal genes regulate resource absorption via the endosperm and embryos, their relative contributions being proportional to their genome ratios in those organs. Excessively high absorption rates result in abortion of seeds but a large embryo (relative to endosperm) is advantageous for germination.
Predictions: Resource absorption directly from the parent by the embryo is favoured if the abortion cost associated with that strategy is relatively low compared with the abortion cost associated with resource absorption by the embryo from the endosperm. Alternatively, the process whereby exalbuminous seeds that mature without direct absorption by the embryo is favoured if the abortion cost associated with resource absorption by the embryo from the endosperm is relatively low and a large embryo is advantageous. Also, it would appear that the difference in the genome ratio between the endosperm (2m : 1p) and the embryo (1m : 1p) affects the ESS: the ESS is not simply the strategy by which a high survival rate of the fertilized ovules during development is realized.
Keywords: albuminous seed, embryo, endosperm, exalbuminous seed, genomic imprinting, intragenomic conflict, resource absorption.
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