Evolution of legumin genes: loss of an ancestral intron at the beginning of angiosperm diversification

Abstract

The polymerase chain reaction was used to survey gymnosperm legumin genes. Characterization of 46 cloned amplificates, differing in sequence and size (1.2-1.6 kb), revealed the ubiquitous occurrence of legumin genes and their organization in small subfamilies in the 22 species investigated. The 3' portions of the genes, coding for the legmnin fi-polypeptides, show a highly conserved intronlexon structure divergent from those of angiosperms: an additional intron (intron IV) uniformly interrupts the region coding for the C-terminal part of the P-polypeptides. Phylogenetic analysis of the respective coding sequences as well as the organization of the Magnolia B14 legumin gene also investigated here both indicate that intron IV is ancestral and was lost during early angiosperm evolution. Taking into account the intronlexon structures from all legumin genes known, our results suggest that legumln genes evolved by subsequent loss of introns, providing also further evidence for a common origin of legumins and vicilins.

Phylogeny, Duplication, and Intraspecific Variation of Adh Sequences in New World Diploid Cottons (Gossypium L., Malvaceae)

“…1). The mechanism(s) responsible for intron loss are not well characterized, although recombination or gene conversion between a cDNA or processed pseudogene and a functional copy is one potential process (Häger et al, 1996;Charlesworth et al, 1998;Drouin and Moniz de Sá, 1997;Loguercio and Wilkins, 1998). The fact that pine Adh sequences share the 10 exon/9 intron structure (Perry and Furnier, 1996) with angiosperms suggests that this configuration is ancestral and that the absence of introns in some sequences represents intron loss.…”

A Molecular-Genetic Study of the Arabidopsis Toc75 Gene Family

“…Interestingly, atTOC75-I appears to have lost a single intron subsequent to its divergence from the other genes. The precise loss of one or more introns has previously been observed in plants and other organisms (Häger et al, 1996;Drouin and Moniz de Sa, 1997). One possible mechanism involves the RT of processed cellular mRNA to produce a cDNA copy of the gene in question, or of a closely related gene, which can then partially replace the genomic copy through homologous recombination or gene conversion (Derr et al, 1991;Drouin and Moniz de Sa, 1997).…”

Sequence Peculiarity of Gnetalean Legumin-Like Seed Storage Proteins

“…The structure of non-crop plant proteins has become available only recently (e.g., Häger et al 1996;. Storage proteins of angiosperms are accumulated mainly in the diploid tissue of cotyledons or the triploid secondary endosperm (for a review see Morton et al 1995).…”

“…The absence of both the first (A) and the third (C) introns in the legumin gene of Welwitschia is a unique situation not found in other legumin genes. The fourth intron (D) first discovered in the gene of Ginkgo legumin (Häger et al 1995) and later described in several other gymnosperm legumin genes (Häger et al 1996) is also found in the legumin gene of Welwitschia mirabilis (Figs. 2 and 3).…”