Fig. 2: Comparative analysis of seed plant intron morphologies.
From: A genome for gnetophytes and early evolution of seed plants
a, Intron length distributions and genome sizes (1C-values, depicted by the relative circle size) are shown for nine representative seed plants. S. lycopersicum, Solanum lycopersicum; G. max, Glycine max. b, Distribution of sequence divergence for four types of TEs in introns of A. trichopoda, G. montanum, P. taeda and G. biloba. The data show that TEs in G. montanum and A. trichopoda are more diverse than in P. taeda and G. biloba. The last two species also show a peak at around 10% sequence divergence probably reflecting a pulse of LTR-RT expansions. c–e, Comparison of orthologous introns between P. taeda (Pta) versus G. biloba (Gbi) (c), P. taeda versus G. montanum (Gmo) (d), and G. montanum versus A. trichopoda (Atr) (e). Two orthologous intron sets that differed more than twofold in length were examined: ‘short’ introns, 0.5–3 kb; and ‘long’ introns, 6 kb. Orthologous introns that were long in one species were also found to be long in the other species of the pair. Analysis of the TEs in orthologous introns showed the long introns of G. montanum and A. trichopoda carried a high proportion of LINEs, contributing to intron expansion. In contrast, gypsy and copia LTR-RT elements contributed most to intron expansion in P. taeda and G. biloba.
