WAAS 2008 – Biotechnology in the Anthropocene
Asexual Seed Formation in Plants
Imran Siddiqi
Centre for Cellular & Molecular Biology
Hyderabad, India
The Sexual Life Cycle
1n
Gametes
2n
2n
Zygote
Adult
Seeds
Apomixis: Asexual Seed Formation
Asexual Reproduction in Animals: Parthenogenesis
•
Asexual Reproduction Occurs Under Conditions
Where Sexual Reproduction is Unfavourable
•
The Capacity for Asexual Reproduction is Embedded
in Sexual Organisms and Has Adaptive Value
Apomixis – Seed Development Without
Meiosis and Fertilization
Apomeiosis – Formation of an unreduced female
gamete (egg).
Parthenogenesis – Development of the egg cell
into an embryo without fertilization by
sperm.
Potential For Apomixis in Plant
Breeding:
• Fixation of genetic character in
successive generations
Hybrid Vigour: Hybrids Show Increased Vigour
But Don’t Breed True
Parent 2
X
Parent 1
Hybrid
P1
F1
P2
Hybrid Vigour
Wheat
10-15%
Rice
20-25%
Selection,
Inbreeding
Apomixis Would Fix Hybrid Vigour Over Successive
Generations
Parent 1
X
P1 Hybrid P2
P1
F1 Parent 2
P1
P2
P1
P2
Potential for Apomixis in Plant
Breeding:
Fixation of genotype (hybrid vigour) –
Nawaschin and Karpachenko (1930)
• Reduced cost of hybrid seed
production
• Successive progagation of hybrids
• Accelerated breeding
• Encourage “risk” in breeding practice
Value of Apomixis
Hybrid Vigour
Wheat
10-15%
Rice
20-25%
Apomixis is rice: 3.4 b$ /yr
Strategies for Transfer of Apomixis
To Food Crops:
Apomixis is a modified sexual
pathway
Genes from sexual plants
Mutation in a gene called DYAD shows female sterility
Normal
dyad mutant
Seeds produced by dyad have an extra set
of chromosomes (triploid)and arise from
fertilization of an unreduced (Apomeiotic)
female gamete
Triploid (3n = 15)
mitosis
No. of plants:
meiosis
17
Diploid (2n = 10)
mitosis
meiosis
2
Conclusion:
Proof of principle demonstration for generating a functional
component of apomixis (apomeiosis) in a sexual plant by altering
a gene of known molecular identity – a first step towards synthesis
of apomixis in crops
Credits:
Maruthachalam Ravi
Bhavna Agashe
V. Subbiah
Gopal Ganesh
CCMB
Funding:
CSIR; Department of Biotechnology;
Mohan P. Anand