MatK Gene Evolution
matK has recently emerged as an invaluable gene in plant systematics due to strong phylogenetic signal compared with other genes used in this field. The matK gene is approximately 1500 bp in length, nested in the group II intron between the 5’ and 3’ exons of trnK in the large single copy region of the chloroplast genome of most green plants. the molecular information generated from matK has been used to resolve phylogenetic relationships from shallow to deep taxonomic levels.
The matK gene stands out among plastid genes used in plant systematics in its distinct mode and tempo of evolution. The rate of substitution in matK is three times higher at the nucleotide level and is six times higher at the amino acid level than that of rbcL. The accelerated rate of amino acid substitution in matK is due to almost even distribution of substitution rates among the three codon positions compared with most protein coding genes where the rates are skewed toward the third codon position.
Our work has gone beyond using the matK gene in systematic studies of the Poaceae, angiosperms and land plants, to attempting to understand the mode of amino acid and protein evolution. We are also conducting functional and structural studies o n the matK and the trnK intron.
(See: Barthet and Hilu 2007, Barthet and Hilu 2008)
Arachis (Fabaceae) Phylogeny and the Evolution of the Peanut Crop
The genus Arachis (Fabaceae) contains approximately 80 wild and crop species native to South America and the peanut crop Arachis hypogaea. Species of Arachis are distributed east of the Andes Mountains and south of the Amazon River, with the most species diversity located in areas around the eastern boarder of Bolivia and western Brazil. The most recent monograph of genus Arachis recognized 69 species, including the crop, dividing them into nine sections based on morphology, geographic distribution and cytogenetics (Krapovickas and Gregory, 1994): Trierectoides, Erectoides, Extranervosae, Triseminatae, Heteranthae, Caulorrhizae, Procumbentes, Rhizomatosae and Arachis. The majority of the Arachis species are diploids, with a basic chromosome number x=10. However, there are five tetraploid species (2n = 4x = 40) including the crop species, and three anueploid species (x=9, 2n = 2x = 18).
The peanut crop, A. hypogaea, is an important economical oil-seed crop that is cultivated in over 100 countries. Other species of Arachis have also been cultivated as indigenous food crop, A. villosulicarpa, and as forage crops, A. glabrata, A. pintoi, and A. repens.
Our work is focusing on the systematics of the genus and the evolution of the tetraploid crop usi ng DNA sequences from chloroplast and nuclear genomic regions.
(See Tallury, Hilu, Milla, Friend, Alsaghir, Stalker, and Quandt, 2005.)
Phalaris (Canary Grass)
Canary grasses belong to the genus Phalaris (Poaceae) and contains 21 annual and perennial species found on five continents: Mediterranean Europe, western Asia, Mediterranean north Africa and southern Africa, North America, and both sides of South America. The species are based on basic chromosome numbers of 6 or 7, and diploids, tetraploids and hexaploids, Our preliminary data and current distribution hint to a potential Mediterranean Europe origin followed by dispersal to West Asia and Africa and the Americas.
Our curresnt research on the genus is in collaboration with Professor Riccardo Baldini of the University of Florence, Italy. We are focusing on extensive field work and molecular phylogenetic and phylogeographic assessments of the evolution of the genus.
Last Updated September 7, 2008
|