The evolution of self-fertility in apomictic plants

Abstract

Self-fertilization and apomixis have often been seen as alternative evolutionary strategies of flowering plants that are advantageous for colonization scenarios and in bottleneck situations. Both traits have multiple origins, but different genetic control mechanisms; possible connections between the two phenomena have long been overlooked. Most apomictic plants, however, need a fertilization of polar nuclei for normal seed development (pseudogamy). If self-pollen is used for this purpose, self-compatibility is a requirement for successful pollen tube growth. Apomictic lineages usually evolve from sexual self-incompatible outcrossing plants, but pseudogamous apomicts frequently show a breakdown of self-incompatibility. Two possible pathways may explain the evolution of SC: (1) Polyploidy not only may trigger gametophytic apomixis, but also may result in a partial breakdown of SI systems. (2) Alternatively, frequent pseudo self-compatibility (PSC) via aborted pollen may induce selfing of pseudogamous apomicts (mentor effects). Self-fertile pseudogamous genotypes will be selected for within mixed sexual-apomictic populations because of avoidance of interploidal crosses; in founder situations, SC provides reproductive assurance independent from pollinators and mating partners. SI pseudogamous genotypes will be selected against in mixed populations because of minority cytotype problems and high pollen discounting; in founder populations, SI reactions among clone mates will reduce seed set. Selection for SC genotypes will eliminate SI unless the apomict maintains a high genotypic diversity and thus a diversity of S-alleles within a population, or shifts to pollen-independent autonomous apomixis. The implications of a breakdown of SI in apomictic plants for evolutionary questions and for agricultural sciences are being discussed.

Study of quantitative genetics of gum arabic production complicated by variability in ploidy level of Acacia senegal (L.) Willd

“…The presence of reproductive barriers is supported by the clear differences in the partitioning of molecular variance within and among families between the two levels of ploidy, which may reflect mating differences as described above. Reproduction with only few male donors and perhaps even self-pollinations and apomixes as suggested for polyploid Ngane is in line with the general observation of selfing and apomixis often being associated with polyploidy (Hörandl 2010). Polyploids are reported to exhibit higher rates of self-fertilization than related diploid species and 99 % of the known apomictic plants are reported to be polyploids (Thompson and Ritland 2006).…”

Polyembryony increases embryo and seedling mortality but also enhances seed individual survival in Handroanthus species (Bignoniaceae)

“…Polyembryony has been described for self-compatible and polyploid populations of Handroanthus chrysotrichus, H. ochraceus and H. serratifolius as a result of pseudogamic sporophytic apomixis with adventitious embryos arising from the hypostasis and ovule integument (Bittencourt Júnior and Moraes, 2010;Bittencourt Júnior and Semir, 2005;Costa et al, 2004;Piazzano, 1998;Sampaio, 2010). The wide geographical distribution observed in Handroanthus ochraceus and H. serratifolius (Gentry, 1992b) is a common feature in polyembryonic and apomictic species, which suggests they may have adaptive advantages over other sexual Handroanthus species (Asker and Jerling, 1992;Hörandl, 2010;Hörandl and Paun, 2007). A complex of apomictic and sexual populations was found for H. ochraceus and H. serratifolius (Barros, 2001;Bittencourt Júnior and Moraes, 2010;Gibbs and Bianchi, 1993;Sampaio, 2010), but the frequency of polyembryonic seeds among populations is still unknown.…”

What does the geography of parthenogenesis teach us about sex?

“…This quirky system is known as gynogenesis in animals [52] and pseudogamy in plants (most parthenogenetic angiosperms [53]). …”