Discovery of plant reproductive success provides insights into human fertility

Researchers have uncovered how successful chromosome segregation during sexual reproduction is achieved in plants.

The discovery, by scientists led by the University of Leicester, could be beneficial for both plant breeding and understanding human fertility.

Eggs and sperm/pollen both carry half the complement of chromosomes that are restored to normal levels upon fertilisation. 

Halving of chromosomes occurs during meiosis, a special cell division, but failure leads to the wrong number of chromosomes in the eggs/sperm/pollen, that may cause miscarriages or rare genetic diseases in humans and infertility in plants.

Faithful chromosome segregation relies on each pair receiving at least one ‘crossover’ event that holds the chromosomes together during meiosis, so crossovers need to be tightly regulated.

In a new study which has just been published in Nature Plants, researchers show that a protein called SCEP3 ensures that crossovers are spread evenly across all chromosomes, thereby preventing mis-segregation and infertility. It does this by limiting the number of crossovers for each chromosome pair, so that there are enough to go round for all. 

For example, in the model plant Arabidopsis thaliana - in the presence of SCEP3 - 15 crossovers may form across five chromosome pairs, so that they receive three each. However, in the absence of SCEP3 some chromosome pairs receive four crossovers and others receive none and this causes chromosomes to be unbalanced during cell division and loss of fertility.

In humans, SIX6OS1 is the equivalent gene of SCEP3, but mutations in humans are difficult to study because cellular errors lead to programmed cell death, whereas plants cells keep living despite defects. 

Therefore, a role for SIX6OS1 in promoting correct chromosome segregation by sharing out crossovers has not been shown, but analysis of SCEP3 suggests that this is likely to be the case. 

Professor  of Plant Genetics James Higgins, lead investigator and corresponding author of the paper from the University's Department of Genetics, Genomics and Cancer Sciences, explained: “Crossovers not only ensure that chromosomes are inherited properly from generation to generation, but also exchange DNA between mother and father chromosomes, so that the child has a new, unique combination of genes. This same process occurs in plants and underpins crop breeding where new combinations of traits are selected. Therefore, this knowledge can be used to produce new crop varieties as well as further investigation into human infertility.”