this ppt made for molecular basis of heterosis of crop plant and it has also incuded heterosis on basis of estimation and genetics basis of heterosis. but these points are not properly explation becarse this ppt main aim to explain the heterosis on the basis of heterosis. thank you....

1. Seminar on
MOLECULAR BASISOF HETEROSISIN CROP
PLANTS
Pradyum Maurya
M.Sc.
Dept. of Genetics and Plant Breeding
DDU Gorakhpur University

2. Content
Introduction
History
Modern view of hybrid vigor
Features of heterosis
Manifestation of Heterosis
Types of Heterosis
On the basis of estimation
Genetic basis of Heterosis
Molecular Mechanism of Heterosis
Transcriptome study
Proteomics studies
Metabolomics
Role of Small RNAs
Epigenomic studies
Conclusion

3. The term heterosis was first used by Shull in 1914.
It is defined as the superiority of F1 hybrid
over both the parents in terms of yield or
some other characters.
Heterosis
Definitionː

4. History
Charles Darwin originally described hybrid vigour in 1876,
and Shull and East independently rediscovered it in 1908,
showing for the first time the great agricultural potential of this
phenomena. Shull adopted the word “heterosis” to simplify and
shorten the phrase “stimulation of heterozygosis.”
Kolreuter identified the heterosis in tobacco hybrids, which he
named after himself.
Heterosis is more common in cross pollinated crops than self
pollinated crops due to he genetic pathways involved in its
expression, which differ greatly across species and also
depending on the kind of pollination used(Chen, 2010).

5. Modern View of Hybrid Vigor
In Brassica napus has higher oil content and better oil
composition than parents.
For viable hybrids, degree of heterosis is proportional to the
parental divergence.
Interspecific hybrids > Intraspecific hybrids
Intersubspp. hybrid > Intrasubspp. (rice)
Not generalized to all hybrids (Maize)
Genetic mechanism of heterosis different between the species
that are Self Pollinated or Cross Pollinated.

6.  Superiority over parents
 Confined to F1
 Genetic control
 Reproducible
 Association with SCA
 Associated with heterozygosity
Features of heterosis

7. Manifestation of heterosis
Increase in yield
Increase in reproductive ability
Increase side and vigour
Better quality
Early flowering and Maturity
More resistant to disease and paste
Grater adaptability
Fast growth rate
Increase in number of a plant parts

8. Types of Heterosis
On the basis of estimation
Average/Relative Heterosis
Heterobeltiosis Heterosis
Economic/Useful/Standard Heterosis
Negative Heterosis

9. Average/Relative Heterosis
It is the heterosis where F1 is superior to mid
parent value. This type of heterosis is no use in
agriculture since the superiority is below the
better parent value.
Where,
𝐹1 = Mean of hybrid
𝑀𝑃 = Mid parent value = (P1+ P2)/2
Average Heterosis =͞F1 − 𝑀𝑃/ 𝑀𝑃 × 100

10. Heterobeltiosis Heterosis
Superiority of F1 over the better
parent.
Where,
𝐵𝑃 = Mean of better parent
Heterobeltiosis Heterosis = 𝐹1 − 𝐵𝑃/𝐵𝑃 × 100

11. Economic/Useful/Standard
Heterosis
Superiority of the F1 compared to the
high yielding commercial variety in a
particular Crop.
Where,
𝐶𝑉 = Mean of commercial variety
Useful Heterosis=𝐹1 − 𝐶𝑉 / 𝐶𝑉 × 100

12. Negative Heterosis
Performance of F1 inferior to better
parent / mid parent value.
e.g.- maturity duration

13. Genetic basis of Heterosis
There are three types of heterosis
1. Dominant hypothesis
2. Over dominance hypothesis
3. Epistasis hypothesis

14. 1.Dominant hypothesis
First proposed by Davenport in 1908. It was later
on expanded by Bruce, Keeble and Pellow in 1910.
Most widely accepted hypothesis of heterosis
According to this hypothesis at each locus the
dominant allele has favorable effect, while the
recessive allele has unfavorable effect.
AA = Aa >aa

15. 2.Over dominance hypothesis
This hypothesis was put forth by Fisher in 1903
and elaborated by East and Shull in 1908 to
explain heterosis.
Over-dominance term was coined by Hull in
1945 working on maize.
Aa > AA or aa
The over dominance hypothesis is also known as
single gene heterosis, cumulative action of
divergent alleles. Fisher (1930) called it
superdominance.

16. 3. Epistasis hypothesis
Gowen (1952), suggested that influence of one
locus on the expression of another may be involved
in heterosis.
It is also known non-allelic interaction.
It is of three types viz. additive x additive,
dominance x dominance and additive x dominance.
Majority of heterotic crosses show epistasis, but
all heterotic crosses do not show epistasis, and all
crosses that show epistasis are not heterotic.

17. Molecular Mechanism of
Heterosis
The genetic evidence coded by diverse gene regulation levels, such
as central of dogma, is the overall output of the genetic information
expressed by numerous gene regulation levels in heterotic
individuals relative to parental inbred lines.
Significant structural and quantitative variety in plant populations
may now be readily quantified because to the development of
modern molecular tools such as single-nucleotide polymorphisms
and next-generation sequencing.
Molecular analysis was performed to assess protein, epigenetic,
transcription, and other gene regulatory components that
contribute to heterosis to investigate the underlying structure that
impacts the degree of hybrid vigour divergence between hybrids
and parental inbreds.

18. Transcriptome Study
The transcriptome analysis of successful parental inbred lines
and hybrids has been carried out in order to categorize diverse
gene expression designs into types of gene activity in a hybrid
combination as opposed to its parental inbred lines, as well as to
link those alterations to improvement in biological yield and
yield production.
To determine if there were any correlations between different
gene expression patterns in many inbred parental lines and
yield-related features of hybrids created by factorial crosses,
transcriptomes from large parental populations were studied
separately.
Gene interaction between the nucleus and the cytoplasm
happens during the hybridization of two inbred parental lines,
resulting in cellular and molecular changes as well as a shift in
gene expression pattern.

19. These alterations in gene expression and genome function in
the F1 hybrid via its inbred parental lines have been seen in a
number of cereal hybrid crops, including maize, wheat and
cotton.
Transcriptome analysis, and its capacity to quantify the
degree of contribution of each allele in hybrid progeny, might
be seen as a transitional phase between phenotypic expression
and genetic information in plants.
Many transcriptome technologies, such as RNA Sequence and
DNA Micro-Array-Based Approaches, will be used to
differentiate parental inbred lines from their hybrid offspring
in order to find gene involvement and impact in heterosis.

20. Proteomics Studies
Additive and non-additive proteomic pattens have been found in
the embryos, roots, nuclei and mitochondria of ear shoots of maize
hybrids, in mature embryos of rice hybrids and in the leaves of
Arabidopsis autopolyploids and allopolyploids.
Findings: Majority of these belongs to functional classes of stress
response
Maize hybrid Zong3/87-1 exhibited an earlier onset or heterosis
in radicle emergece.
The dry and 24h imbibed embryos detached from seeds were
used for protein extraction
Differential proteomic analysis between hybrid and its parental
lines was performed.

21. Metabolomics
Biomass heterosis is correlated with increased levels of metabolic
activity, in case of Thalana intraspecfic hybrids.
The maternal contribution of nutrients and metabolites to growth
vigour is consistent with the parent-of-origin effect on biomass
vigour in reciprocal hybrids
14-20 metabolites were sufficient to predict freezing tolerance
among different F1 hybrids, and they explained 60% of the variance.
Compatible solutes in the pathway leading to raffinose are crucial
indicators of freezing tolerance heterosis.
Limited numbers of particular metabolites provide useful
biomarkers for the prediction of heterosis.

22. Role of Small RNAs
Most sRNAs are derived from TEs and Repeats, thus have diverged between spp.
Differences in sRNA levels between hybrids of allopolyploids and their parents
could alter allelic patterns of expression, RNA directed DNA methylation and
overall genomic stability.
sRNAs generated by the RNA interference pathway can target homologous
genomic DNA sequences for cytosine methylation through a process called RdDM.
sRNA show expressional variation in allotetraploids and hybrid as compared to
their parents.
24-nucleotide sRNAs guide the de novo methyltransferase DRM2 to homologous
loci to establish DNA methylation, which leads to transcriptional silencing.

23. Epigenomic Studies
When two distinct parental inbred lines are crossed, epigenetic
changes such as histone acetylation, chromatin remodeling ,
modest RNAi regulation, and DNA methylation occur.
In most crop species, DNA methylation is the most essential
regulator of genome-related activity and cellular development.
The overall frequency of DNA methylation in hybrids varies
according to the genetic variety of the parental inbred lines.
The repressing initiated transcription pathway, which either
blocks the regulatory genetic causes of inbreeding depression or
promotes gene expression for heterosis, is primarily responsible
for the appearance of heterosis through DNA methylation.

24. Conclusion
Heterosis is result of interacting genomes, resulting in complex
changes at the genetic, epigenetic, biochemical and regulatory
network levels.
Epigenetic regulation of circadian-mediated changes in
chlorophyll biosynthesis and starch metabolism offers one of the
direct links to growth vigor in plant hybrids.
Availability of novel genetic and genomic tools, that allow for
the integrated study of the complex interactions between
genome organization and expression might contribute to a
better understanding of heterosis.

25. You...