Testing a Role for Rop9 GTPase in Maize Pollen Tube Growth

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Testing a Role for Rop9 GTPase in Maize Pollen
Tube Growth

• Lauren A. Osborn
• Dr. John Fowler
• Botany and
• Plant Pathology
• Summer 2005

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Pollen Tube Growth

• Pollination and pollen tube growth is essential
• fertilization
• seed production in plants
• Two phases for pollen tube growth in Maize
• Germination
• Growth in the silk

Pollen Tubes
Germination
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Corn Life Cycle
Pollen Grains
Silk and Egg
Mature Adult
Fertilization
Seedlings
Seed
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Rop Genes

• Nine different Rop genes in maize
• ROP GTPases are proteins that act as a signaling
  molecule (example pollen tube growth)

• Rop2 mutant pollen has a reduced ability to
  fertilize

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My Research Rop9 gene
ATG
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Unusual Inheritance

• Previous analysis on a Rop9 mutant corn ear had
  more wild type kernels
• Also the kernels were distributed with more
  mutants at the top

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m



Less mutants expected if mutation affects pollen
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Hypothesis

• Rop9 affects pollen tube growth in silk
• Mutant pollen at a disadvantage competing with
  wild type to fertilize

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Predictions

• Pollen tubes from Rop9 mutant pollen grains will
  grow more slowly
• If pollen tube growth is affected Rop9 mutants
  would have a disadvantage at reaching kernels at
  the bottom of the ear

Short silks
Long Silks
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Experiments

• There are two ways to test for the role of Rop9
  in pollen tube growth
• Indirectly and Directly

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The Indirect Test

• Test through genotyping kernels by PCR
• Test top and bottom of maize ears
• Genotype kernels at top and bottom

Top
Rop9 Wild type band
Bottom
Rop9 Mutant bands
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Rop9 Result Totals
Wild Type vs. Mutant
Ear 1
Ear 2
Ear 5
Ear 4
Ear 3
m1
m6
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Ear 1
Ear 2
Ear 4
Ear 5
Ear 3
m1
m6
Results do not confirm top and bottom prediction
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The Direct Test

• Use fresh pollen
• Microscope imaging to observing pollen tube
  growth
• See directly whether mutant pollen grains
  germinate or grow pollen tubes more slowly than
  wild-type pollen grains

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Pollen Germination on Media
Light wild type Dark mutant
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Results from Direct Test I
Percent Germination
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Results from Direct Test II
Pollen Tube Length
1 Hour
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Summary

• Rop9 has an effect on pollens ability to carry
  out fertilization
• However my results do not confirm a role for Rop9
  in pollen tube growth

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Future Research

• Initial hypothesis Pollen Tube Growth
• Possibly may have an effect on late events
• Fertilization?

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Acknowledgements

• Ernest and Pauline Jaworski Fund
• Howard Hughes Medical Institute
• Dr. Kevin Ahern
• Dr. John Fowler
• Zuzana Vejlupkova
• Rex Cole
• Kirsten Carol
• Darin Olson