Developmental Evolution of the Sexual Process in Ancient Flowering Plant Lineages

Third-codon transversion rate-based Nymphaea basal angiosperm phylogeny -- concordance with developmental evidence

“…Due to limited availability of sequenced chloroplast genomes, we recognize that the 36 land plant taxa compiled by Qiu et al (2006) do not include some less derived members of certain taxa, particularly other members in the ANITA grade, e.g., Schisandraceae, Austrobaileya, Trimeniaceae. However, since all members in the ANITA clade except Amborella show similar female reproductive structures (Williams and Friedman 2002;Friedman and Williams 2003;Friedman and Williams 2004;Friedman 2006), representation by Nymphaea for all non-Amborella members of ANITA is warranted.…”

“…The best tree in Qiu et al (2006) . The reconciliation of the P 3 Tv-based molecular phylogeny (A) and the corresponding evolution of female gametophyte (B) and ploidy of endosperm (C) (Williams and Friedman 2002;Friedman and Williams 2003;Friedman and Williams 2004;2006). During double fertilizations, the central cell is fused with a sperm cell (1n), producing diploid (2n) endosperm in Nymphaea, and triploid (3n) endosperm in Amborella and the non-ANITA angiosperms.…”

“…Therefore, the discordance among the trees appears to be mainly caused by systematic errors as different reconstruction methods consistently generate discordant, yet highly supported trees (Stefanovic, Rice, and Palmer 2004;Chang et al 2006;Jansen et al 2006;Jeffroy et al 2006;Qiu et al 2006). Moreover, the inability to separate Amborella and Nymphaea in Amborella plus Nymphaea co-basal phylogeny suggests the current molecular phylogenetic signals used in the inference are not robust enough to reconcile the evolutionary history of angiosperms (Williams and Friedman 2002;Friedman and Williams 2003;Friedman and Williams 2004;Friedman 2006).…”

“…From the ancestral gymnosperms, containing multiple egg cell megagametophytes yielding haploid embryo nourishing tissues upon a single fertilization event, the earliest angiosperm (all ANITA except Amborella) evolved into a 4-cell/4-nucleus female gametophyte (a single developmental module) which yielded a diploid endosperm upon double fertilization. In the early angiosperm history, this basic module was duplicated and resulted in 8-cell/9-nucleus female gametophyte in Amborella or 7-cell/8-nucleus one in the non-ANITA angiosperms, both of which yielded a triploid endosperm upon double fertilization (Friedman and Williams 2003;Friedman and Williams 2004;Friedman 2006). This hypothesis thus places non-Amborella ANITA members (represented by Nymphaea in most studies) as representative of the most basal angiosperms, thus conflicting with the current Amborella-basal (or Amborella plus Nymphaeales co-basal) molecular phylogeny.…”

“…Concurrently, developmental biologists have studied two key developmental aspects in the ANITA clade, i.e., the structure of female gametophyte and formation of embryo nourishing tissue (endosperm), to help clarify the origin of the extant angiosperms (Williams and Friedman 2002;Friedman and Williams 2003;Friedman and Williams 2004;Friedman 2006). All ANITA members except Amborella have a 4-cell/4-nucleus female gametophyte with one of the double fertilization events yielding a biparental diploid endosperm (Williams and Friedman 2002;Friedman and Williams 2003;Friedman and Williams 2004), whereas the rest of angiosperm species have an 8-cell/9-nucleus (Amborella) (Friedman 2006) or a 7-cell/8-nucleus (all non-ANITA angiosperms) female gametophyte, with one of the double fertilization events yielding a biparental triploid endosperm (Friedman and Williams 2003;.…”