this assignment provide the information about to types of organeller DNA their features and their inheritance and expression

1. Department of Plant Breeding and Genetics
Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (M.P.)
(2017-18)
Assignment
On
Inheritance and Expression of Organeller DNA
Presented by :
Sarla Kumawat
Ph.D. 1st year
Professor
V.K. Gour

2. Inheritance and Expression of Organeller DNA
History of Organeller DNA
 1908– Correns, first presented the evidence for
cytoplasmic inheritance in Mirabilis jalapa.
 1908-Baur, first presented the evidence for cytoplasmic
inheritance in Pelargonium zonale.
 1924 Jenkins, described the iojap leaf variegation in
maize.
 1933 Rhodes, described CMS in Maize
 1943 Sonneborn ,kappa particle in Paramoecium

3.  Organellar DNA also known as maternal DNA. It
is of two types i.e. Mitochondrial and chloroplast
DNA.
Important features of Organellar DNA
 Replicates both in chloroplast and mitochondria
in a semi-conservative fashion.
 Liable to mutation.
 They are expressed and inherited separately
from nuclear genes.
 They are transcribed and translated within the
organelles.
 Uni-parental inheritance is observed.

4.  Present in multiple copies in each organelle cp-DNA- 20-
40 copies per chloroplast, ~4 copies per mitochondria
(E.g.: Yeast).
1. Mitochondrial DNA:
 May be circular or linear.
 Size: varies from ~16.5kb to ~100kb.
 Human mitochondrial genes contain no introns,
although introns are found in the mitochondria of other
groups (plants, for instance).
2. Chloroplast DNA
 Double-stranded
 Chloroplasts contain naked circular DNA.

5.  Circular, super coiled, and generally not associated
with any proteins.
 Size: Varies. 85kb (Codium fragile) to 2000kb
(Acetabularia sp.), Larger than mitochondrial
genomes (80-600 Kb in length).
 Each chloroplast contains 10-60 (sometimes 100)
copies of its genome. The gene controlling
cytoplasmic inheritance are present outside the
nucleus and in the cytoplasm, they are known as
plasma gene, cytoplasmic genes, extra chromosomal
genes.
 The sum total of genes present in cytoplasm of a cell
is known as Plasmon.
 All the genes present in a plastid are known as
Plastoms.

6. Structure of Chondriome Structure of Plastidome

7. Organeller Inheritance
 Organeller inheritance are true cytoplasmic
inheritance, concerned with either chloroplast or
mitochondrial traits and are usually associated with
their DNA.
Features of Organellar Inheritance
 Governed by organellar genes
 Does not exhibits distinct segregation pattern
 Reciprocal differences are observed
 Show maternal effects
 Mapping is difficult
 Plasma genes are associated with either cpDNA or
mtDNA.

8. Important features of Organellar Inheritance
 Reciprocal differences - As organellar genome
from only on parent, generally the female parent
are transmitted (Uni-parental inheritance).

9.  Lack of Segregation
 Irregular Segregation in Biparental Inheritance
 Somatic Segregation
 Association with Organellar DNA
 Mutagenesis
 Lack of Association with A Parasite, Symbiont or
Virus
Plastid inheritance: Carl Correns (1908) Studied
the inheritance of leaf variegation called
‘albomaculatus’ in the four O clock plant
Mirabilis jalapa.

10. Variegated-shoot phenotypes in four o’clocks
Mixed chloroplasts
White/green
Mutant chloroplast
White
non-photosynthetic
Normal chloroplast
Green
photosynthetic

12. MITOCHONDRAL INHERITANCE
 Inheritance pattern governed by mt-DNA is
termed as mitochondrial inheritance.
Examples of Mitochondrial inheritance are as
follows:-
 Cytoplasmic Male Sterility in plants
Maize,Sorghum etc.
 Pokyness in Neurospora
 Petite in Yeast

13. Expression of Organeller DNA
Expression of mitochondrial DNA
 Mitochondrial DNA (mtDNA), which encodes
subunits of the oxidative phosphorylation complexes
essential for cellular respiration and ATP production.
 Expression, replication, and maintenance of mtDNA
require factors encoded by nuclear genes.
 These include not only the primary machinery
involved (eg. transcription and replication
components) but also those in signaling pathways
that mediate or sense alterations in mitochondrial
function in accord with changing cellular needs or
environmental conditions.

14.  The basic protein machinery required for
transcription initiation in human mitochondria has
been elucidated after the discovery of two
multifunctional mitochondrial transcription factors, h-
mtTFB1 and h-mtTFB2, that are also rRNA
methyltransferases.
 For example, in the D-loop regulatory region there are
four sequence elements (conserved sequence blocks:
CSB I, CSB II, CSB III; and origin of H-strand synthesis:
OH) that are postulated to be important for initiation of
transcription-primed, leading-strand DNA synthesis
according to the asymmetric model of mtDNA replication.

15.  This site lies in an unusual region of the
genome where there is a clustering of five
adjacent tRNA genes. Although this site is a
major region of initiation of lagging-strand
synthesis, it appears that other sites on the
molecule may serve as alternative initiation
sites.
 Third, one of the first features of mtDNA to be
recognized is the D-loop itself. This is a stable
three-stranded DNA structure of ∼570 to 665
nucleotides in length (in humans) that begins at
OH and extends downstream where it ends at a
few distinct sites.

16.  These elements are downstream of the LSP and
are involved in configuring and processing the
LSP transcript to form RNA primers for initiation
by the mtDNA polymerase, Pol γ.
 Therefore, the RNA primers for leading-strand
mtDNA replication are generated by POLRMT
(the mitochondrial RNA polymerase). Second,
approximately two-thirds the distance around the
mtDNA molecule from OH is OL, which is a
primary site of initiation of lagging-strand mtDNA
synthesis, according to the asymmetric
replication model.

17.  This structure has all of the features of a stalled (or
terminated) leading-strand replication intermediate;
however, whether this is actually the case has not been
strictly determined.
 Since its discovery, the significance of the need to
maintain this structure in a subset (a large subset in
some cells) of mtDNA molecules has eluded the field, but
it is logical to assume it is of regulatory importance with
regard to expression, replication, and/or inheritance of
mtDNA.

18.  With regard to regulation of mtDNA expression and
maintenance, a key point to re-emphasize is that, except
for the mtDNA-encoded rRNAs and tRNAs, all of the
factors required for transcription, RNA processing,
translation, replication, and repair of mtDNA are encoded
by nuclear genes, translated by cytoplasmic ribosomes,
and imported into mitochondria to their sites of action.
 In other words, there is an important and relatively large
subset of the ∼1500 nucleus-encoded proteins in the
mitochondrion that is devoted to mitochondrial gene
expression and mtDNA maintenance.
 Signalling pathways must exist to coordinate the activities
of these distinct genetic compartments (the nucleus and
mitochondria) to maintain and modulate mitochondrial
gene expression.

19.  Chloroplast gene expression
 Chloroplast genomes of extant land plants have only
50 protein-coding genes involved in photosynthesis,
gene expression, lipid metabolism and other
processes, 30 tRNA genes and full sets of rRNA genes.
 In spite of their small genomes (0.15 Mbp in land plant
chloroplasts versus 3 Mbp in cyanobacteria),
chloroplast gene expression is regulated by more
complex systems compared to the simple prokaryotic
regulatory system.
 Chloroplast gene expression is mediated by two
distinct types of RNA polymerase (RNAP) and is
highly dependent on post-transcriptional regulation.

20.  such as the processing of polycistronic transcripts,
intron splicing and RNA editing. Moreover, recent
RNA-sequences analyses of chloroplast transcripts
identified unexpected diversifications of RNA
molecules, such as non-coding and antisense RNAs
(Hotto et al., 2011 and Zhelyazkova et al., 2012)
 However, the genes encoded in chloroplast
genomes are insufficient to regulate their
complicated gene expression, and so the chloroplast
gene expression machinery includes various
nucleus-encoded regulatory components.
 Chloroplast gene expression is largely dependent on
prokaryotic machineries derived from the ancestral
cyanobacterium.

21.  The bacterial multi-subunit RNAP is composed of a
core Rpo complex, which has the catalytic enzyme
activity, and a sigma factor, which recognizes
promoter sequences (Ishihama, 2000). Chloroplasts
contain the bacterial-type RNAP, called plastid-
encoded plastid RNAP (PEP), which shares
functional similarity with the bacterial RNAP (Igloi
and Kossel, 1992;

22. Significance of organeller DNA
 Role cytoplasmic organelles in transmission
of characters.
 mapping of chloroplast and mitochondrial
genome.
 cytoplasmic male sterility.
 Mutation of chloroplast-DNA and
mitochondrial-DNA leads to generation of
new variants.
 mt-DNA is used for the study of human
evolution.