Angiosperm origin and early stages of seed plant evolution deduced from rRNA sequence comparisons

Abstract

Complete or partial nucleotide sequences of five different rRNA species, coded by nuclear (18S, 5.8S, and 5S) or chloroplast genomes (5S, 4.5S) from a number of seed plants were determined. Based on the sequence data, the phylogenetic dendrograms were built by two methods, maximum parsimony and compatibility. The topologies of the trees for different rRNA species are not fully congruent, but they share some common features. It may be concluded that both gymnosperms and angiosperms are monophyletic groups. The data obtained suggest that the divergence of all the main groups of extant gymnosperms occurred after the branching off of the angiosperm lineage. As the time of divergence of at least some of these gymnosperm taxa is traceable back to the early Carboniferous, it may be concluded that the genealogical splitting of gymnosperm and angiosperm lineages occurred before this event, at least 360 million years ago, i.e., much earlier than the first angiosperm fossils were dated. Ancestral forms of angiosperms ought to be searched for among Progymnospermopsida. Genealogical relationships among gymnosperm taxa cannot be deduced unambiguously on the basis of rRNA data. The only inference may be that the taxon Gnetopsida is an artificial one, and Gnetum and Ephedra belong to quite different lineages of gymnosperms. As to the phylogenetic position of the two Angiospermae classes, extant monocotyledons seem to be a paraphyletic group located near the root of the angiosperm branch; it emerged at the earliest stages of angiosperm evolution. We may conclude that either monocotyledonous characters arose independently more than once in different groups of ancient Magnoliales or that monocotyledonous forms rather than dicotyledonous Magnoliales were the earliest angiosperms. Judging by the rRNA trees, Magnoliales are the most ancient group among dicotyledons. The most ancient lineage among monocotyledons leads to modern Liliaceae.

WITHDRAWN: TcJAMYC: A bHLH transcription factor that activates paclitaxel biosynthetic pathway genes in yew

“…This regulator has been named Taxus cuspidata JAMYC (TcJAMYC). There is similarity in sequence and function between TcJAMYC and the wellcharacterized AtMYC2, indicating a conserved response to MJ despite at least 150 million years of divergence between the angiosperm and gymnosperm lineages (21). The results presented here suggest that TcJAMYC is a key candidate gene for engineering increased paclitaxel accumulation in Taxus cell cultures.…”

A Novel Auxin Conjugate Hydrolase from Wheat with Substrate Specificity for Longer Side-Chain Auxin Amide Conjugates

“…Monocots diverged from dicots approximately 200 to 250 million years ago (Wolfe et al, 1989;Troitsky et al, 1991;Kellogg, 2001). Therefore, IAR3 must predate this point of divergence, since it is conserved not only in the angiosperms but in the gymnosperms as well (Campanella et al, 2003c).…”

“…Therefore, IAR3 must predate this point of divergence, since it is conserved not only in the angiosperms but in the gymnosperms as well (Campanella et al, 2003c). The gymnospermangiosperm divergence took place 300 to 360 million years ago, suggesting that the ILR1-like family is quite ancient and that its role is intimately tied to growth and development in vascular plants (Troitsky et al, 1991;Oliviusson et al, 2001;Albert et al, 2002;Cooke et al, 2002Cooke et al, , 2004.…”

A Gymnosperm Extensin Contains the Serine-Tetrahydroxyproline Motif

“…Hence, we mooted the possibility that extensins containing Ser-Hyp4 blocks might be more representative of advanced herbaceous dicots rather than primitive dicots and advanced graminaceous monocots. On the other hand, if we consider possible very early angiosperm origins and monocot-dicot divergence (20,28), then the single C-terminal Ser-Hyp4 of maize THRGP may mean that Ser-Hyp4 blocks are a conserved primitive feature; if that were so, we predicted their presence in gymnosperm extensins (1 1).…”

“…Hence, we mooted the possibility that extensins containing Ser-Hyp4 blocks might be more representative of advanced herbaceous dicots rather than primitive dicots and advanced graminaceous monocots. On the other hand, if we consider possible very early angiosperm origins and monocot-dicot divergence (20,28), then the single C-terminal Ser-Hyp4 of maize THRGP may mean that Ser-Hyp4 blocks are a conserved primitive feature; if that were so, we predicted their presence in gymnosperm extensins (1 1).A cell suspension culture isolated from Douglas fir, Pseudotsuga menziesii (Mirbel), yielded two salt-elutable cell surface HRGPs identified as monomeric extensins differing in size (8). The larger monomer was a PHRGP that lacked SerHyp4, but it did contain the general repetitive motif Pro-Hyp-X-Y-Lys similar to that of the repetitive Pro-rich proteins of dicots (2,5,7,8,19).…”