Behind a great man there is always a great woman, but when the woman is a mother, she is always ahead.
In flowering plants, the beginning of embryogenesis is almost exclusively governed by maternal gene activity. This finding was reported by an international team of researchers including plant geneticists from the University of Zurich. It was obtained using next generation sequencing technology. This newly uncovered mechanism may be involved in the maintenance of species boundaries and could play an important role in the development of novel crop varieties.
Mother and father each contribute one half of the genetic information to their offspring. Thus, it was thought that both parents contribute equally to the development of the next generation. Indeed, this holds true for late stages of embryo development in plants, but early on, things are quite different: during the earliest phase of embryo development predominantly the maternal genes are active. A mother always knows what´s the best for her son, so this phase of development is controlled largely by maternal factors, which actively repress or silence the genes inherited from the father. She wears the pants.
The Zürich scientists crossed two genetically distinguishable races of the model plant Arabidopsis thaliana and analyzed the relative contributions of the parental genomes shortly after the first division of the fertilized egg. Such molecular genetic analyses of plant embryos at very early stages are technically challenging, which explains why up to now researchers resorted to studying embryos at later stages. Grossniklaus, Professor for Plant Developmental Genetics at University of Zurich, and colleagues were able to show that in an early phase of plant embryo development, predominantly maternal genes are active. Via siRNAs, the maternal genome controls paternal genes to ensure that, initially, most remain inactive. In the course of development, paternal genes are successively activated, which also requires the activity of maternal factors. This finding suggested that these siRNAs have a specific role in preventing transposons to move within the genome.
The mother invests considerable resources into the formation of seeds. Before making this investment, the mother verifies the paternal contribution to the progeny for compatibility with her own genome. If the father's genome is too divergent from her own, e.g., originating from a different species, the embryo will die. Maternal control may ensure the maintenance of species boundaries. Genetic incompatibility will cause embryos to abort, such that fertilization with pollen from other plant species is not successful. This may also explain why attempts to
cross crop plants with their wild relatives, e.g., to transfer disease-resistance genes present in wild relatives to crops, often fail early in embryogenesis.
Commercial crop breeders will thus be interested in finding out how the maternal control of early plant embryo development can be circumvented in their breeding programs.
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Carlota Rey Casal
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