Organellar heterosis - Mitochondria and chloroplast

1. Organellar Heterosis and Complementation
Submitted by:
B.Rachana
RAD/2018-18
PhD (GPBR)
Submitted to:
Dr. M.V. Nagesh Kumar
Professor
Dept. of GPBR
GP- 507 Heterosis Breeding

2. What is Organellar genome?
• Organelle – Mitochondria, chloroplast,
Golgi, ER etc.
• The genome present in chloroplast and
mitochondria are called as Organellar
genome.

3. Organellar Genome
MITOCHONDRIAL DNA CHLOROPLAST DNA

4. History of Organellar Genome
1962 1963
Ris and Plaut
First
demonstrated
presence of
DNA in
chloroplast.
Nass & co workers
Provedthe
existence of DNA
in
mitochondrion

5. 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.
• Present in multiple copies in each organelle. cp-
DNA- 20-40 copies per chloroplast. ~4 copies
per mitochondria (E.g.: Yeast).

6. Difference Between Organellar DNA and
Nuclear DNA
Organellar DNA
• Found in chloroplast and
mitochondria.
• Usually circular except
in ciliate protozoa,
where it is linear.
• Synthesis continues
throughout cell cycle.
Nuclear DNA
• Found in chromosomes.
• Linear in eukaryotes and
circular in prokaryotes.
• Synthesis continues only
during interphase.

7. Heterosis is not simply because of heterozygosity
Heterosis phenomenon includes
• Increased growth
• Increased development
• Better differentiation
• Better metabolism
All these genes will interact to lead to heterosis.
Nuclear genome is responsible but mitochondria
and chloroplast also have DNA.

8. Mac Key (1976) classified Heterosis
Genomic Heterosis
(originates from
nuclear genes)
Plasmatic Heterosis
(originates from
plasmagenes)
Mitochondrial Heterosis Chloroplast Heterosis

9. Characteristics of Mitochondrial Genome
• May be circular or linear.
• Size: varies from ~16.5kb to
~100kb.
• mt-genome shows larger variation in
size compared to that of chloroplast.
• Mitochondria must be closely
associated with manifestation of
heterotic effects particularly in
physiological processes like cellular
metabolism, respiration and energy
conversions for growth.

10. Characteristics of Chloroplast Genome
• Chloroplasts contain naked
circular DNA. 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.

11. Organelle Heterosis and Complementation –
Mitochondrial Heterosis
• The involvement of mitochondria in heterosis is judged
by respiratory function and higher enzyme activities in
the hybrids.
• Mitochondrial complementation- the enhanced
oxidative phosphorylation efficiency of artificially mixed
mitochondria of certain inbreds (in maize seedlings).
• The more vigorous varieties of maize and soybean have
more tightly coupled mitochondria than the less
vigorous varieties.
• Mitochondrial ATP:0 ratios in wheat seedlings are
correlated to seed metabolism, which is in turn
determined by the metabolic activity of the plant during
formation and maturation of the seeds.

12. • Positive correlation between seed and oil yield
and mitochondrial activity in oil palm has been
observed.
• Hybrid mitochondria possess an abundance of
lipid-phospholipid, linoleic acid in their fatty acid
fraction and a higher amount of internal “bound”
water during heterotic expressions.
• Mitochondrial complementation and grain yield
in hybrid wheat showed correlation between F1
yield heterosis and mitochondrial efficiency.
• All these observations are in accordance with the
view that mitochondria plays a significant role in
the manifestation of heterosis.

13. Chloroplast Heterosis
• Chloroplast heterosis i.e. higher photosynthetic rates,
have also been observed in the seedling stages.
• The term “chloroplast complementation” is generally used
to indicate the greater activity of 1:1 parental mixture of
isolated chloroplasts when compared to the mid- parental
values.
• Hybrids are characterized to possess highly developed
fine structure of mitochondria and chloroplast than their
respective parents.
• The increase in size of the lamellae and thylakoid
membrane structure in the chloroplast of the hybrid was
directly correlated with their chlorophyll contents.

14. • The enhanced activities of the key enzymes of
the Calvin cycle in hybrid chloroplasts,
heterosis in chlorophyll content in maize and
sorghum has been reported.
• The enhanced activities due to chloroplast
complementation were also found to be
closely associated with the degree of grain
yield heterosis.
• These observations on chloroplast heterosis
and complementation, just like mitochondrial
complementation, suggest that hybrids are
endowed with efficient conservation of
energy in their organelles.

15. Organellar Heterosis and Complementation
in Higher plants
Parameters Plant species
Cytochrome oxidase Wheat (Triticum aestivum)
Oxidative phosphorylation (ADP: 0 ratio)
Wheat (Triticum aestivum) Maize (Zea
mays)
Respiratory control index ( State 3 / state 4
oxidation ratio)
Maize (Zea mays)
Barley (Hordeum vulgare) Soybean
(Glycine max) Pea (Pisum sativum)
Cytochrome and phospholipid contents Wheat (Triticum aestivum)
Chloroplast heterosis and complementation
Ribulose biphosphate Carboxylase/oxygenase Maize (Zea mays)
Sorghum (Sorghum vulgare) Barley
(Hordeum vulgare)
Photophosphorylation Maize (Zea mays)
Cotton (Gossypium hirsutum)
Chlorophyll content Wheat (Triticum aestivum) Soybean
(Glycine max) Maize (Zea mays)

16. Intergenomic Interaction and
Organelle Complementation
• Intergenomic interaction between nuclear and organelle
genes is a dominant theme in heterosis
• Organelle heterosis is the result of complementation
between polymorphic mitochondria and chloroplast,
which may be transmitted biparentally in the F1 hybrid.
• Mechanism of heterosis at the level of mitochondria and
chloroplast would involve complementation of proteins
or polypeptide subunits encoded by both nuclear and
organelle genes having non-additive gene effects instead
of unique nuclear genome.
• The resulting products due to intergenomic interaction in
organelles of hybrid organisms ensure for enhanced
structural and catalytic functions of these organelles.

17. Interspecific Complementation and
Heterosis
• Organelle polymorphism can result from recombination
between organelle genomes derived from the paternal
and maternal sources due to biparental transmission.
• In parasexual hybrids, chloroplasts from both parents
may stay together and be distributed to daughter cells,
with one type of chloroplast dominating the other.
• Mitochondria isolated from the seedlings of the hybrids
and their parents showed different efficiencies of
oxidative phosphorylation during ATP synthesis.
• The mitochondira from the non-heterotic hybrids had
the same phosphorylative efficiency as that of the
parents was considered as an expression of heterosis.

18. Conclusion
• Superior mitochondrial and chloroplast functions caused
by both genomic and intergenomic complementation are
considered as essential components of heterosis.
• Intergenomic interaction in mitochondira and chloroplast
of hybrid organisms would ensure for enhanced structural,
catalytic, and regulatory functions leading to heterosis and
adaptive advantage.
• Recombinant DNA technology have opened up the
possibility not only of a greater understanding of heterosis
as a phenomenon but of its directed utilization to make
agriculture highly productive and efficient in terms of
resource utilization and environmental cost.

19. Creation of male sterility through GE
and its exploitation in Heterosis

20. Transgene
• A transgene is a gene or genetic material that
has been transferred naturally or by any of a
number of genetic engineering techniques
from one organism to another.
• The introduction of a transgene has the
potential to change the phenotype of an
organism.

21. Transgenic Male Sterility
• When the male sterility is induced by the techniques
of genetic engineering, it is called as transgenic male
sterility.
• It is heritable and basically comes under genetic
male sterility.
• In this system, the two kinds of genes are
involved.
• One gene causes male sterility (integrated with
genome of A line) while the other suppresses it (in
R line).

22. • Transgenes may be used to produce GMS
which is dominant to fertility.
• In these cases it is essential to develop
effective fertility restoration systems for
hybrid seed production.
• An effective restoration system is available in
at least one case, Barnase/Barstar system.

23. BARNASE/BARSTAR SYSTEM FOR
ENGINEERED MALE STERILITY
 Barnase is extracellular RNase
 barstar is inhibitor of barnase
 Fuse the barnase and barstar genes to TA29 promoter
 TA29 is a plant gene that has tapetum specific
expression
 Plants containing the TA29–barnase construct are male
sterile
 Cross male sterile (barnase) with male fertile (barstar) to
get hybrid seed.

24. Mariani et al ,1992

27. Features
• Efficient fertility restorer system
• Easy maintenance of male sterile lines
• Easy elimination of a male fertile plants from
male sterile lines
• Lack of adverse affects on other traits
• Stable male sterile phenotype over different
environments
• Satisfactory performance of F1 hybrids

28. SELECTED TRANSGENES USED FOR
PRODUCTION OF MALE STERILITY
TRANSGENE SOURCE TRANSGENIC
PLANT
rolC A.rhizogenes Tobacco,potato,
DTA Diptheria pathogen Tobacco
barnase Bacillus
amyloliquefaciens
Tobacco, B.napus
Rnase T1 Aspergillus oryzae Tobacco,oilseed,rape
Chalcone synthase
gene antisense
construct
Petunia Petunia ,tobacco
Chalcone synthase
cDNA
Petunia petunia
rolB A.rhizogenes Tobacco
Bcp1 Brassica campestris B.oleracea
(B.D.Singh, 2005)