Ploidy and the Evolution of Endosperm of Flowering Plants

Abstract

In angiosperms, spermatozoa go by pair in each pollen grain and fertilize, in addition to the egg cell, one of its sister cells, called the central cell. This ''double fertilization'' leads to the embryo on the one hand and to its nutritive tissue, the endosperm, on the other hand. In addition, in most flowering plants, the endosperm is triploid because of a doubled maternal genetic contribution in the central cell. Most of the hypotheses trying to explain these eccentricities rest on the assumption of a male/female conflict over seed resource allocation. We investigate an alternative hypothesis on the basis of the masking of deleterious alleles. Using analytical methods, we show that a doubled maternal contribution and double fertilization tend to be favored in a wide range of conditions when deleterious mutations alter the function of the endosperm. Furthermore, we show that these conditions vary depending on whether these traits are under male or female control, which allows us to describe a new type of male/female conflict.

Fitness Landscapes: An Alternative Theory for the Dominance of Mutation

“…For instance the genetic load with inbreeding (e.g., Whitlock 2002), the magnitude of inbreeding depression (e.g., Bataillon and Kirkpatrick 2000;Charlesworth and Willis 2009), the rate of adaptation in diploids (e.g., Orr and Otto 1994), the evolution of mating systems (e.g., Epinat and Lenormand 2009), dispersal (e.g., Roze and Rousset 2005), life cycles (e.g., Otto and Goldstein 1992), polyploid tissues (e.g., Cailleau et al 2010), and sex (e.g., Agrawal 2009) depend on the distribution of dominance of mutations, to cite a few; there are other situations where dominance matters (Charlesworth and Charlesworth 1998;Lynch et al 1999).…”

Kin recognition within a seed and the effect of genetic relatedness of an endosperm to its compatriot embryo on maize seed development

“…In the vast majority of angiosperms, the endosperm and embryo are genetically identical except for ploidy (2)(3)(4)(5)(6). The embryo is diploid, but the endosperm is triploid and is composed of one paternal gametophyte genome and two identical maternal gametophyte genomes that are derived from the two polar nuclei in the central cell (1).…”

Enhancer Runaway and the Evolution of Diploid Gene Expression

“…Before discussing the implications and predictions associated with this theory, it is useful to relate it to previous models involving variation in dominance, ploidy, mutation load and selection for modifiers. It shares with models of ploidy evolution the fact that increased haploid expression leads to more efficient purging of deleterious mutations, which benefits tightly linked modifiers [ 38 , 39 ]. It shares with models of dominance evolution [ 45 – 48 ] the limit that selection on modifiers is weak, of the order of the mutation rate (even if this issue may be alleviated if migration is the source of deleterious alleles [ 48 , 49 ]).…”

“…The deterministic change in frequency at the enhancer locus can be computed from standard population genetics equations, considering a generic diploid life cycle with four steps: diploid selection, meiosis with recombination, mutation and syngamy. This frequency change can be decomposed into two terms that correspond to ‘masking’ and ‘purging’, as introduced in previous related models [ 38 , 39 ] (see derivation in methods ). The ‘masking’ term does not depend on recombination, and is frequency-dependent.…”