Faculty of Science, School of Sciences, Natabua Campus Lautoka BIO706 Embryology Lecture 23: Asexual Seed Formation in Plants - III

The Sexual Life Cycle 1n Gametes 2n 2n Zygote Adult Seeds

Apomixis: Asexual Seed Formation

Asexual Reproduction in Animals: Parthenogenesis

Where Sexual Reproduction is Unfavourable 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. Apomixis is found in several plant species and can occur by different developmental mechanisms. There are two major components of apomixis: Apomeiosis and Parthenogenesis.

Potential For Apomixis in Plant Breeding: Fixation of genetic character in successive generations Navashin and Karpachenko in the 1930s pointed out that the transfer of apomixis to crop plants held many benefits to agriculture

Hybrid Vigour: Hybrids Show Increased Vigour But Don’t Breed True Parent 2 Parent 1 X Hybrid Selection, Inbreeding F1 P2 P1 Hybrid Vigour 10-15% 20-25% Wheat Rice

Apomixis Would Fix Hybrid Vigour Over Successive Generations Parent 1 P2 P1 Hybrid P2 P1 P2 P1 F1 P1 Parent 2 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 Navashin and Karpachenko in the 1930s pointed out that the transfer of apomixis to crop plants held many benefits to agriculture

Value of Apomixis Hybrid Vigour 10-15% Wheat 20-25% Rice Apomixis in 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 We isolated several mutants and one of them which we named dyad is shown here. Dyad shows female specific sterility. Pollen development is normal The ovule is the precursor of the seed and the wild type ovule contains the female gametophyte which is haploid and formed by postmeiotic divisions of one of the spores formed after meiosis. It contains the egg cell and associated cells that are required for fertilization, embryogenesis, and seed development. The reason for sterility in the mutant is immediately apparent because it lacks the entire female gametophyte and instead contains two enlarged cells where the gametophyte would normally be found.

2 No. of plants: Seeds produced by dyad have an extra set of chromosomes (triploid)and arise from fertilization of an unreduced (Apomeiotic) female gamete mitosis meiosis Triploid (3n = 15) Diploid (2n = 10) No. of plants: 17 2

Proof of principle demonstration for generating a functional 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

Questions are welcome