Chloroplast genome analysis of Angiosperms and phylogenetic relationships among Lamiaceae members with particular reference to teak (Tectona grandis L.f)

Abstract

Availability of comprehensive phylogenetic tree for flowering plants which includes many of the economically important crops and trees is one of the essential requirements of plant biologists for diverse applications. It is the first study on the use of chloroplast genome of 3265 Angiosperm taxa to identify evolutionary relationships among the plant species. Sixty genes from chloroplast genome was concatenated and utilized to generate the phylogenetic tree. Overall the phylogeny was in correspondence with Angiosperm Phylogeny Group (APG) IV classification with very few taxa occupying incongruous position either due to ambiguous taxonomy or incorrect identification. Simple sequence repeats (SSRs) were identified from almost all the taxa indicating the possibility of their use in various genetic analyses. Large proportion (95.6%) of A/T mononucleotide was recorded while the di, tri, tetra, penta and hexanucleotide amounted to less than 5%. Ambiguity of the taxonomic status of Tectona grandis L.f was assessed by comparing the chloroplast genome with closely related Lamiaceae members through nucleotide diversity and contraction/expansion of inverted repeat regions. Although the gene content was highly conserved, structural changes in the genome was evident. Phylogenetic analysis suggested that Tectona could qualify for a subfamily Tectonoideae. Nucleotide diversity in intergenic and genic sequences revealed prominent hyper-variable regions such as, rps16-trnQ, atpH-atpI, psc4-psbJ, ndhF, rpl32 and ycf1 which have high potential in DNA barcoding applications.