Mitochondria and chloroplasts are eukaryotic organelles that evolved from bacterial ancestors and harbor their own genomes. The gene products of these genomes work in concert with those of the nuclear genome to ensure proper organelle metabolism and biogenesis. Organelle genomes occur in a variety of sizes and topologies.
|PLANT||B. campestris||218||multiple circles|
|Z. mays||570||multiple circles|
- Describe the organization and coding content of modern-day organelle genomes
- Reconcile any discrepancies between observed DNA structures and the physical maps
- Describe how evolution has shaped and changed modern-day organelle genome coding content compared to ancestral prokaryotic genomes
- Consider the possible reasons that plant organelles retain genomes at all
- Explain the challenges and experimental opportunities associated with genetic transformation of the plastid genome
- Small but essential for functional advantages
- Multiple organelles per cell, multiple genomes per organelle
- 20 - 20,000 genomes per cell depending on cell type
- Organized in nucleo-protein complexes called Nucleoids
- Non-Mendelian inheritance pattern
- Maternal inheritance is followed but not always
- Necessary but not sufficient to elaborate a functional organelle
- Nuclear gene products required for their function
- Genes of these organelles are translated on cytosolic ribosomes
- Then imported into the organelles
- Plant mitochondria also import tRNAs
The availability of the complete plastid genome sequence should facilitate improved transformation efficiency and foreign gene expression in crops through utilization of endogenous flanking sequences and regulatory elements (Ruhlman et al, 2006 ).
The advantages of plastid transformation for bioengineering are several-fold
- Integration of multiple genes in a single transformation event (Lossl et al., 2003),
- Lack of gene silencing (Dhingra et al., 2004),
- Position effect due to site-specific transgene integration (Daniell et al., 2002)
- Minimization of pleiotropic effects due to compartmentalization of recombinant proteins (Daniell et al., 2001)
Genomics of CWR generates data that support the use of CWR to expand the genetic diversity of crop plants. Advances in DNA sequencing technology are enabling the efficient sequencing of CWR and their increased use in crop improvement. As the sequencing of genomes of major crop species is completed, attention has shifted to analysis of the wider gene pool of major crops including CWR. A combination of de novo sequencing and resequencing is required to efficiently explore useful genetic variation in CWR. Analysis of the nuclear genome, transcriptome and maternal (chloroplast and mitochondrial) genome of CWR is facilitating their use in crop improvement (Brozynska et al., 2016). In addition to improving our understanding of plant biology and evolution, chloroplast genomics research has important translational applications, such as conferring protection against biotic or abiotic stress and the development of vaccines and biopharmaceuticals in edible crop plants (Daniell, 2016). Genome analysis results in discovery of useful alleles in and identification of regions of the genome in which diversity has been lost in domestication bottlenecks. Targeting of high priority CWR for sequencing will maximize the contribution of genome sequencing of CWR. Coordination of global efforts to apply genomics has the potential to accelerate access to and conservation of the biodiversity essential to the sustainability of agriculture and food production.
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Research Scholar at Genetics and Plant Breeding, BHU