MONOGENIC INHERITANCE OF APOMIXIS IN TWO HIERACIUM SPECIES WITH DISTINCT

DEVELOPMENTAL MECHANISMS

Genetics and Plant breeding-Fall 2011

Publication By

Ahmed ElFatih ElDoliefy

R. A. BICKNELL

Plant Sciences, NDSU, ND, USA

Presented by

N. K. BORST A. M. KOLTUNOW

Heredity 84 (2000) 228-237

Studying Genetics

TraitConclus

ion

Data Analysis and Results

Experimental Design and

Data Collection

Organism

THE TRAIT

asexual formation of seed (genetically uniform progeny), yet the genetic mechanisms that control this trait remain unclear

APOMIXIS (APOSPORY)

Megaspore mother cell

• Embryo sac = n• Normal fertilization• Somatic embryo (2n)

from nucellus replaces sexual embryo

• Take over the endosperm (= pseudogamous)

• Facultative mechanism – Either sexual or asexual seeds are formed

Diplospory

Adventitious embryony

Normal meiosis

Apospory• A normal (n) embryo sac• Another diploid embryo

sac may develop from a nucellus cell

• Both develop endosperms following fertilization (pseudogamous)

• Poly-embryony• A facultative mechanism

n

Normal meiosis

Non-reduction division

2n n

• No fertilization (2n egg develops in an embryo)

• Non-pseudogamous (autonomous) endosperm development (from polar nuclei)

• Meiotic diplospory/ mitotic diplospory

2n

nucellus

THE HYPOTHESIS

The trait is inherited through a single dominant gene

The Trait can pass through the diploid and haploid male gametes

Gametophytic apomixis is asociated with polyploidy

Studying Genetics

TraitConclus

ion

Data Analysis and Results

Experimental Design and

Data Collection

Organism

THE ORGANISM

Two apomictic species of Hieracium with two different forms of mega-gametogenesis.

H. aurantiacum H. piloselloides H. pilosella

Two apomictic biotypes of Hieracium were used, 1- Triploid accession (2n=27, x=9) of H. piloselloides (designated `D3')2- Aneuploid accession (2n=3x+4=31) of H. aurantiacum (designated `A3.4').

Both produce high degree of fertile haploid pollen

How can we detect that hybrid is success …! Morphological markers (traits)…

1- bright orange flowers of H. aurantiacum2- upright form and strap-shaped leaves of H. piloselloides

Two sexual biotypes were used; 1- Tetraploid accession of H. pilosella from Caen, France (designated `P4') 2- Anther culture-derived diploid (Bicknell & Borst, 1996) of P4 (designated `P2')

Both P4 and P2 appear to be self-incompatible under cool winter conditions

PLANT MATERIALS

If embryos were detected the plant was scored as a putative apomict.

If embryos were absent but embryo sacs were present normally , the plant was scored as sexual.

If degenerate structures were seen the plant was scored as sterile.

If flowers either failed to form or developed abnormally. These plants were also scored as sterile.

For scoring and collecting data

Apomixis was defined as the formation of an embryo(s) at petal senescence following the decapitation of an immature capitulum.

For scoring and collecting data

In apomictic biotypes of Hieracium maternal embryos arise spontaneously before the final senescence of the flower (stage 10 in Koltunow et al., 1998).

•In sexual types, prevention of fertilization by bud decapitation (Koltunowetal.,1995) leads to the retention of aquiescent mature embryo sac up until this developmental stage, so that differences between sexual and apomictic types could be readily determined

This measure is a score of parthenogenesis rather than apomixis as a whole as it does not include a measure of meiosis.

chi-squared test for a fixed ratio hypothesis with application of the Yates's continuity correction factor to compensate for the low number of observations in some data sets.

S F

A a b NA

B c d NB

NS NF N

For a 2 × 2 table with the following entries:

some cases, this is better.

Yates corrections for continuity to testing for independence in a contingency table

Data Analysis and Results

Studying Genetics

TraitConclus

ion

Data Analysis and Results

Experimental Design and

Data Collection

Organism

BREEDING SCHEME FOR APOMIXIS INHERITANCE To avoid apomixis difficulties crosses were designed using the apomict as the staminate parent and the sexual plant as the recipient.

The triploid progeny (3x) resulted from the union of a haploid gamete from the pistillate parent, with a diploid gamete from the staminate parent. Since, no plants were obtained with a chromosome number greater than 27, it appears that completely unreduced gametes did not contribute to the formation of this population.

WHICH MEANS …

Backcrosses were conducted to determine which F1 category class (3x -apo, or 3x- sex.) represented the homozygous recessive.

The 2 (2x) were sterile, whereas the 30 (3x) BC1 plants segregated for apomixis similar to the F1 population

BC of (3x) sexual F1 plant to the sexual parent yielded only sexual progeny

Sexuality looks to be the phenotype of the homozygous recessive genotype

GOOD NOTICE …

Poor recovery of (2x) in the cross (D3 and P2), shows a bias against survival of products following the involvement of haploid, male gametes.

Q: Is it occur at the level of haploid gamete viability/efficacy, or of (2x) zygote survival.

A: a cross (P4 and D3) was made …

The (2x) P2 was originally derived by anther culture from P4, so the P2 genome represented a subset of P4. So that

The (3x) in this cross should be union of a (2x) egg (from P4) with a (1x) sperm nucleus (from D3)

…REMEMBER…

SO THAT…

Apomixis segregated among both the (3x) and (4x) F1 progeny.

WHICH MEANS …

Χ2 test consisted with the expected ratio and proposed that (1x) gametes could transmit the dominant allele conferring apomixis in this system

The apomictic F1 BC resulted in a segregating population, with ratios of apomictic and sexual biotypes similar to the F1.

While the sexual F1 BC resulted in only sexual and sterile progeny.

To test allelism it was necessary to combine the 2 dominant alleles in a single plant by crossing, also one of the apomicts used as a recipient parent

Of the 10 hybrids, 4 were (4x), 4 were (3x) and 2 were aneuploids ( 3x+4 and 3x+5). All were either apomictic or sterile.

2 of the (4x), set many germinable seeds. The best of these plants, designated `AD4', was test-crossed to the sexual (2x) P2 and the (3x) progeny scored for apomixis.

Which means … that sterility does not appear to be preferentially associated with either apomixis or sexuality.

However, close linkage, possibly allelism, is indicated as the most probable genetic model.

Conclusion Authors used hybridization between parents and also back crosses in their experiment

The research paper could be used as one of the applications for polyploidies, to study genetics, and in this specific case, segregating progenies of apomixis.

Back crosses were used to test for inheritance of the dominant alleles in polyploidy

Apospory in H. piloselloides and H. aurantiacum was inherited as a monogenic, dominant trait.

Both D3 and A3.4 were simplex for the dominant allele at the Apo locus.

Sexuality is the homozygous, recessive phenotype, which will lead to the dispersion of dominant alleles.

The identification of 2 polyploids each bearing a single dominant allele at Apo locus is consistent with the expectation arise rarely in this taxon.

The dominant factors of A3.4 and D3 are closely linked

Terms used in this presentation

Pistillate

Staminate

Ideotype

Back crosses

Test crosses

Biotypes

Apomixis

Triploid

Aneuploidy