Asexual Seed Formation in Plants

Centre for Cellular & Molecular BiologyHyderabad, India

Imran Siddiqi

WAAS 2008 – Biotechnology in the Anthropocene

The Sexual Life Cycle

Adult

Gametes

Zygote

Seeds

2n2n

1n

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

Parent 1X Hybrid

Selection,Inbreeding

F1 P2P1

Hybrid Vigour

10-15%

20-25%

Wheat

Rice

F1P1 Parent 2

Parent 1

Apomixis Would Fix Hybrid Vigour Over Successive Generations

P2P1 Hybrid P2P1 P2P1

X

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

Hybrid Vigour

10-15%

20-25%

Wheat

Rice

Apomixis is rice: 3.4 b$ /yr

Value of Apomixis

Strategies for Transfer of Apomixis To Food Crops:

Apomixis is a modified sexualpathway

Genes from sexual plants

Normal dyad mutant

Mutation in a gene called DYAD shows female sterility

Seeds produced by dyad have an extra setof chromosomes (triploid)and arise from

fertilization of an unreduced (Apomeiotic) female gamete

mitosis mitosismeiosis meiosis

Triploid (3n = 15) Diploid (2n = 10)

No. of plants: 17 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 synthesisof apomixis in crops

Credits:

CCMB Funding:CSIR; Department of Biotechnology;

Maruthachalam Ravi

Mohan P. Anand

Bhavna AgasheV. SubbiahGopal Ganesh