Methods of transforming somatic cells of maize haploid embryos

1. A method of transforming a somatic cell of an isolated maize haploid embryo with a polynucleotide of interest using Agrobacterium -mediated transformation and treating the transformed cell with a chromosome doubling agent to produce a transgenic homozygous plant cell, wherein said maize haploid embryo is produced by crossing a selected female parent with a male inducer line.

2. The method of claim 1 , wherein a growth stimulation polynucleotide has been introduced into the female parent or male inducer line by stable or transient transformation.

3. The method of claim 2 wherein the growth stimulation polynucleotide encodes RepA or Lec1.

4. The method of claim 1 wherein the male inducer line contains a scorable marker gene operably linked to an embryo-preferred promoter.

5. The method of claim 1 further comprising regenerating a transgenic homozygous plant from the transgenic homozygous plant cell.

6. A method of producing a stably transformed double haploid maize plant comprising:

a) pollinating a maize plant with pollen from a haploid inducer line, wherein said haploid inducer line comprises a marker gene that is expressed in maize embryos at the early developmental stage,

b) obtaining maize embryos that are haploid, wherein:

i. one or more maize kernels resulting from step (a) are identified as containing marker negative embryos, thus identifying haploid maize embryos, and said haploid maize embryos are isolated from the maize kernels; or

ii. isolating maize embryos from maize kernels resulting from step (a) and identifying marker negative embryos, thus identifying haploid maize embryos,

c) stably transforming a cell of a haploid maize embryo obtained in (b) with a polynucleotide of interest using Agrobacterium -mediated transformation to form a transformed maize cell,

d) growing transformed callus from the transformed maize cell,

e) treating the transformed callus with a chromosome doubling agent to produce a stably transformed double haploid maize cell, and

f) regenerating said double haploid maize cell into a double haploid maize plant.

7. The method of claim 6 , wherein a growth stimulation polynucleotide has been introduced into the maize plant that is pollinated in step (a) or the haploid inducer line by stable or transient transformation.

8. The method of claim 7 wherein the growth stimulation polynucleotide encodes RepA or Lec1.