Current trends in chloroplast genome research

Abstract

Chloroplast is an important cellular organelle of autotrophs which has an independent, circular, doublestranded DNA molecule termed as chloroplast genome. The chloroplast DNA (cpDNA) contains essential genes for its maintenance and operation. Several components of the photosystems and proteins involved in biosynthetic pathways are also encoded by the chloroplast genome. Exploring the genetic repository of this organelle is vital due to its conserved nature, small size, persistent gene organization and promising ability for transgenic expression. Therefore, cpDNA sequence information has been instrumental in phylogenetic studies and molecular taxonomy of plants. Chloroplast genome sequencing efforts have being initiated with conventional cloning and chain-termination sequencing technologies. Dedicated databases such as CGDB and GOBASE among others have been established as more and more complete cpDNA sequences are being reported. Presently, elegant molecular biology techniques including shotgun sequencing, rolling circle amplification (RCA), Amplification, Sequencing and Annotation of Plasteome (ASAP) and Next generation sequencing are being used to accelerate data output. Owing to many fold increase in submission of cpDNA sequences in nucleotide databases, challenges of in-depth data analysis stimulated the emergence of devoted annotation, assembling and phylogenetic software. Recently, reported bioinformatics software for chloroplast genome studies comprise of DOGMA for annotation, SCAN-SE, ARAGON and PREP suit for RNA analyses and CG viewer for circular map construction/comparative analysis. Faster algorithms for gene-order based phylogenetic reconstruction and bootstrap analysis have attracted the attention of research community. Current trends in sequencing strategies and bioinformatics with reference to chloroplast genomes hold great potential to illuminate more hidden corners of this ancient cell organelle.