Molecular evolutionary characterization of an Activator (Ac)-like transposable element sequence from pearl millet (Pennisetum glaucum) (Poaceae)

Abstract

We present data on the evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). A defective Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and its entire 4531 bp sequence has been determined. When the pearl millet Ac-like sequence is aligned with the maize Ac sequence, it is found that there is approximately 70% DNA similarity in the central region spanning most of maize Ac exon II and all of exon III. In addition, there are two smaller regions of similarity at the Ac terminii. Besides these three major structural similarities, Pennisetum Ac has two large regions, one 5' and one 3', that show little similarity to Zea Ac. Furthermore, most of the sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between the central region of maize and pearl millet Ac sequences is estimated to be 0.429 +/- 0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395 +/- 0.051 nucleotide substitutions per site. If we assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. Conserved DNA and amino acid sequence motifs are also examined. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25-40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet and have thus existed in the grasses for at least 25 million years.

Rice Transposable Elements: A Survey of 73,000 Sequence-Tagged-Connectors

“…3A). Rice STC OSJNBa0076F14f is probably a rice ortholog of Activator, because the branching pattern of maize, pearl millet, and rice is the same as would be expected from a species phylogeny (Macrae et al 1990(Macrae et al , 1994Paterson et al 1996). Clearly, the rice STC OSJNBa0005B04f is a paralog of Activator and may have diverged from the line leading to Activator and snapdragon Tam3 early in plant evolution.…”

Transposition-Based Plant Transformation

“…Various plant species have been shown to contain elements that belong to the Ac-Ds family. Such elements include Tip100 of common morning glory (Ipomoea purpurea; Ishikawa et al, 2002), Pac1 of pearl millet (Pennisetum glaucum;MacRae et al, 1994), and various elements in sugar cane (Saccharum officinarum;de Araujo et al, 2005). Furthermore, it may be possible to employ other transposable element systems, such as Arabidopsis (Arabidopsis thaliana) Tag1 (Frank et al, 1997) and maize En-Spm (Kumar et al, 2005).…”

The hAT family: a versatile transposon group common to plants, fungi, animals, and man

“…3, some subgroups possess high bootstrap values, indicating a high probability for the correctness of this Schultes et al (2000) subbranching. This is particularly true for the Pac1 and Ac9 elements from Pennisetum glaucum (MacRae et al 1994) andZ. mays (Pohlmann et al 1984a, b) and for the Tag1 (Tsay et al 1993) and Bg (Hartings et al 1991) transposons from Arabidopsis thaliana and Z. mays, respectively, which have bootstrap values greater than 90.…”