Scientists at the University of Birmingham have identified an elusive male gene in the field poppy that stops self–fertilization, a mechanism that prevents inbreeding, and promotes greater genetic diversity.
Plant biologists had already uncovered that poppies prevent self-fertilization when a female gene on the stigma tells it which pollen to accept or reject, triggering several chemical signals to stop pollen tube growth. However, the corresponding “label” on pollen that allows recognition of “self” remained elusive.
Now the team, funded by the Biotechnology and Biological Sciences Research Council, have discovered the sought after male gene – PrpS – which specifies pollen recognition and so regulates self-incompatibility. This gene works with the female S component that controls the pistil (the plant’s female reproductive organ) to decide whether the flower can accept or reject pollen. This breakthrough may also provide a new way to produce F1 hybrid crops, which could be a major boost for plant breeders.
Professor Noni Franklin-Tong of the School of Biosciences, said: “Finding this pollen component is a major breakthrough for us. Flowers recognize self and non-self pollen through a genomic region known as the S locus, which comprises a male and a female gene (in the pollen and pistil); these interact to allow ‘self recognition’. We already had the female S component identified, and now we have found the other half to this ‘lock and key’: the elusive male pollen component, in this important cell-cell recognition and rejection system.
“This is a major achievement for us as it unlocks the mystery as to how poppy specifies recognition of ‘self’ pollen ”
This is a hat-trick for the team, with the third published study about the sexual reproductive systems of poppies in the prestigious journal, Nature, in 5 years. The team’s long-term goal is to establish how the different components integrate and interact in what has turned out to be a complex signalling network. Now they have solved a major part of the poppy’s reproductive puzzle.
Most flowering plants run the risk of pollinating themselves, rather than receiving pollen from another plant via an insect. The basic anatomy of many plants means pollen sacs are situated next to the female reproductive parts. Accidental self-fertilization is a real risk. When a flowering plant is pollinated, the pollen germinates and develops a pollen tube which grows through the stigma and female tissues and then enters the plant’s ovary to effect fertilization. If this involves self pollen, it results in inbreeding, which can result in a shrinking gene pool and unhealthy offspring.
Previously, the Birmingham team found that when genetically identical pollen comes into contact with the field poppy’s stigma, the interaction triggers several chemical signals for inhibiting growth of the pollen tube. With tube growth halted, fertilization cannot take place. Another mechanism then kicks in, with a mechanism called “programmed cell death” resulting in incompatible pollen being told to commit suicide. This ensures that unwanted pollen tubes do not make seed.
The current studies used a novel cell culture technique that was developed in Birmingham, to prove that the male gene was responsible for this specific inhibition of pollen. A small “antisense” molecule corresponding to part of the pollen S gene was added to this culture to show that this specifically interfered with self pollen inhibition.
Genetic diversity in plant science is vitally important for the breeding of new varieties of crops. By using generic traits, preserved over generations by mechanisms such as this, plant breeders are able to develop new varieties to help meet demands for more yield, with less input, on less land and in the face of a changing climate. Without such approaches, the world will not be able to meet the challenge of the growing food security crisis.
Identification of the pollen self-incompatibility determinant in Papaver rhoeas will appear on www.nature.com on 31 May 2009 at 1800 BST London time/1300 US Eastern time.
Any members of the media wishing to speak to Prof. Franklin Tong on 30 or 31 May should contact Ben Hill, University of Birmingham Press Officer, on 07789 921163.
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Notes to Editor:
The research team of Mike Wheeler, Barend de Graaf, Natalie Hadjiosif, Ruth Perry, Natalie Poulter, Kim Osman, Sabina Vatovec, and Andrea Harper, were led by husband and wife co-PIs, Professor Chris Franklin and Professor Noni Franklin-Tong
The University of Birmingham’s School of Biosciences is based in the College of Life and Environmental Sciences.
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