Generation of haploid plants

1. A plant having biological activity of a haploid inducer and comprising a nucleotide sequence encoding a centromere histone H3 (CENH3) protein comprising a CATD domain, wherein the nucleotide sequence comprises a mutation encoding a polypeptide having one or more amino acid substitutions at positions 1, 4, 8, 10, 22, 25 and 26 of an α2-helix consensus sequence, wherein said alteration confers the biological activity of a haploid inducer, wherein the plant is homozygous with respect to the mutation and is not able to express a native CENH3 protein, and

wherein the α2-helix consensus sequence comprises A, P, V or L at position 1; E, D, Q, H or L at position 2; A at position 3; L or V at position 4; V, L, M, I, R, Y or T at position 5; S or A at position 6; Q at position 8; E at position 9; A or S at position 10; A or T at position 11; E at position 12; D, N, F, I or Y at position 13; Y, F or H at position 14; L, I or V at position 15; V or I at position 16; G, R, E, H, N, T, E, D or Q at position 17; L, M or I at position 18; F, M or L at position 19; S, E, D or G at position 20; D, M, V, N, E, A, R or K at position 21; S, G, A or T at position 22; M, W, N or H at position 23; L or H at position 24; C or L at position 25; A or T at position 26; L or I at position 27; H at position 28; and A or S at position 29.

2. The plant according to claim 1 , wherein crossing between the plant and a wildtype plant or a plant expressing wildtype CENH3 protein yields at least 0.1% haploid progeny.

3. The plant according to claim 1 , wherein the nucleotide sequence comprising the mutation is an endogenous gene or a transgene.

4. The plant according to claim 3 , wherein the nucleotide sequence comprising the mutation is a transgene.

5. The plant according to claim 1 , wherein the one or more amino acid substitutions comprise:

a substitution for the amino acid A, P, V or L at position 1 of the α2-helix consensus sequence;

a substitution for the amino acid L or V at position 4 of the α2-helix consensus sequence;

a substitution for the amino acid Q at position 8 of the α2-helix consensus sequence;

a substitution for the amino acid A or S at position 10 of the α2-helix consensus sequence;

a substitution for the amino acid A at position 22 of the α2-helix consensus sequence;

a substitution for the amino acid C or L at position 25 of the α2-helix consensus sequence; and

a substitution for the amino acid A or T at position 26 of the α2-helix consensus sequence.

6. A part of the plant according to claim 1 comprising a mutation causing in the CATD domain an alteration of the amino acid sequence at position 4 of the α2-helix sequence of the α2-helix consensus sequence.

7. A method of generating a haploid plant, comprising the steps of:

a) crossing a plant according to claim 1 to a plant expressing wildtype CENH3 protein, and

b) identifying the haploid progeny plant generated from the crossing step.

8. A method of generating a double haploid plant, comprising the steps of:

a) crossing a plant according to claim 1 to a plant expressing wildtype CENH3 protein,

b) identifying a haploid progeny plant generated from the crossing step, and

c) converting the haploid progeny plant into a double haploid plant.

9. A method of facilitating a cytoplasm exchange, comprising the steps of:

x) crossing a plant according to claim 1 as ovule parent with a plant expressing wildtype CENH3 protein as pollen parent, and

y) obtaining a haploid progeny plant comprising the chromosomes of the pollen parent and the cytoplasm of ovule parent.

10. A method of generating a plant according to claim 1 , comprising the steps of:

i) subjecting seeds of a plant to a sufficient amount of the mutagen ethylmethane sulfonate to obtain M1 plants,

ii) allowing sufficient production of fertile M2 plants,

iii) isolating genomic DNA of M2 plants and

iv) selecting individuals comprising said nucleotide sequence comprising said one or more mutations of the α2-helix consensus sequence, wherein said substitution confers the biological activity of a haploid inducer, and wherein the plant is homozygous with respect to the mutation and is not able to express a native CENH3 protein.

11. An isolated nucleotide sequence encoding a centromere histone H3 (CENH3) protein comprising a CATD domain, wherein the nucleotide sequence encodes a polypeptide having substitutions at one or more of positions 1, 4, 8, 10, 22, 25 and 26 of an α2-helix consensus sequence of SEQ ID NO: 1.

12. A vector comprising the nucleotide sequence of claim 11 .

13. A plant cell or a host cell comprising the nucleotide sequence of claim 11 , or a vector comprising said nucleotide sequence, as a transgene.

14. A method of generating a transgenic plant comprising the steps of:

yy) transforming a plant cell with the nucleotide sequence of claim 11 , or a vector comprising said nucleotide sequence, and

zz) regenerating a plant having the biological activity of a haploid inducer from the plant cell.

15. The part of the plant according to claim 6 , wherein the part is a shoot vegetative organ, root, flower or floral organ, seed, fruit, ovule, embryo, plant tissue or cell.

16. The plant according to claim 1 , wherein the one or more mutations comprise:

a T at position 1 of the α2-helix sequence of the α2-helix consensus sequence; a F at position 4 of the α2-helix sequence of the α2-helix consensus sequence; a stop codon or a L at position 8 of the α2-helix sequence of the α2-helix consensus sequence; a T at position 10 of the α2-helix sequence of the α2-helix consensus sequence; a T at position 22 of the α2-helix sequence of the α2-helix consensus sequence; a Y at position 25 of the α2-helix sequence of the α2-helix consensus sequence; and/or a V at position 26 of the α2-helix sequence of the α2-helix consensus sequence.