Evolution Of Poaceae Chloroplast Genome

Chloroplasts, which are semi‐autonomous organelles in plant cell, have their own genome. The chloroplast genomes(cpDNA) are highly conserved in organization with most plant plastid genomes composed of a single circular doublestranded DNA molecules. With the development of DNA sequencing technology, over 70 species chloroplast DNA were sequenced completely. The most recent studies of cpDNA were focused on the sequencing of new plastid genomes with comparison among relative genomes. The investigation of neighbor‐dependent mutation in chloroplast has developed for a few years. However, these studies are short of more complete chloroplast genomes and the influence from non‐adjacent sites.In our study, we counted the numbers of various dinucleotides in five Poaceae cpDNA, wheat(Triticum aestivum), barley(Hordeum vulgare), rice(Oryza sativa), maize(Zea mays) and sorghum(Sorghum bicolor), to examine whether dinucleotide bias exists in plastid genome. We next identified the relationship between mutation patterns and the base composition of flanking sites, which is assessed using classical chi‐square tests, by comparing five Poaceae cpDNA pairwise, using Phalaenopsis aphrodite as the outgroup. To find out the relationship between base composition of adjacent sites and the Chi‐square values for different dinucleotides, we counted the substitutions to and from each dinucleotide. seven of which show consistent substitution trends in all comparison results taken into accout. Dinucleotides substitution trends are influenced by nucleotide substitutions, and it seems that the lose of A and T and the gain of C and G would be the future direction of evolution.