Floral homeotic genes were recruited from homologous MADS-box genes preexisting in the common ancestor of ferns and seed plants

Abstract

Flowers sensu lato are short, specialized axes bearing closely aggregated sporophylls. They are typical for seed plants (spermatophytes) and are prominent in f lowering plants sensu stricto (angiosperms), where they often comprise an attractive perianth. There is evidence that spermatophytes evolved from gymnosperm-like plants with a fern-like mode of reproduction called progymnosperms. It seems plausible, therefore, that the stamens͞carpels and pollen sacs͞nucelli of spermatophytes are homologous to fern sporophylls and sporangia, respectively. However, the exact mode and molecular basis of early seed and f lower evolution is not yet known. Comparing f lower developmental control genes to their homologs from lower plants that do not f lower may help to clarify the issue. We have isolated and characterized MADS-box genes expressed in gametophytes and sporophytes of the fern Ceratopteris. The data indicate that at least two different MADS-box genes homologous to f loral homeotic genes existed in the last common ancestor of contemporary vascular plants, some descendants of which underwent multiple duplications and diversifications and were recruited into novel developmental networks during the evolution of f loral organs.

The MADS-domain protein PPM2 preferentially occurs in gametangia and sporophytes of the moss Physcomitrella patens

“…In pteridophytes, which are the closest sister group of seed plants, MADS-box genes are predominantly active in both vegetative and generative structures of sporophytic tissues; additional gametophytic expression is more exceptional (Münster et al, 1997;Hasebe et al, 1998;Münster et al, 2002). MIKC c MADS-box genes in seed plants are nearly absent from gametophytic tissues.…”

“…One important finding for the reconstruction of the evolutionary history of the MADS-box gene family was the identification of angiosperm gene orthologs in gymnosperms showing a high degree of functional conservation (Sundström & Engström, 2002). So far MIKC c MADS-box genes have been characterized from different representatives of lycophytes (Svensson & Engström, 2002;Tanabe et al, 2003), pteridophytes (Münster et al, 1997;Hasebe et al, 1998;Münster et al, 2002), bryophytes (Krogan and Ashton, 2000;Henschel et al, 2002;Hohe et al, 2002) and green algae (Tanabe et al, 2005). However, no evidence for the existence of seed plant gene orthologs could be obtained from non-seed plants.…”

Cycads: evolutionary innovations and the role of plant-derived neurotoxins

“…Two reports mention that MADS box genes have been cloned in Zamia [37] and in Cycas [40], but expression data has not been reported. The ABC lineage is missing from ferns [41], therefore cycads need to be analyzed to explore the origins of the ABC genes to confirm or refute B and C gene expression patterns found in Gnetum and Conifers.…”

Selection on Length Mutations After Frameshift Can Explain the Origin and Retention of the AP3/DEF-Like Paralogues in Impatiens

“…Floral homeotic class B genes, which comprise AP3/DEF and PI/GLO, are required for petal identity in the second whorl and stamen identity in the third whorl of eudicot flowers (Jack et al 1992(Jack et al , 1994Goto and Meyerowitz 1994;Theissen et al 2000;Alvarez-Buylla et al 2000). AP3/DEF belong to the type II class MADSbox genes, consisting of four distinct regions: a MADS domain (M), an intervening region (I), a keratine-like domain (K), and a C-terminus (C) (Munster et al 1997). The MADS domain is essential for binding DNA to CarG promoter sequences.…”