Under cold conditions, not only the mother plant but also the parent plant can pass on chloroplasts to the offspring – ScienceDaily

Scientists at the Max Planck Institute for Molecular Plant Physiology in Potsdam (Germany) have analyzed for the first time the inheritance of chloroplasts under a wide range of environmental conditions. Contrary to the prevailing view that chloroplasts are only transmitted by the parent plant, parental chloroplasts can also be transmitted to the offspring under cold conditions. Thus the maternal and paternal chloroplasts meet in the offspring and may be able to exchange genetic material with each other. The new findings may allow plant breeders for the first time to selectively use traits from the chloroplast genetic material.

The story of flowers and bees is the classic introduction to a topic still rarely discussed in our society: sex in plants! When plants reproduce, the sperm inside the pollen grain fuses with the egg cell inside the flower on which the pollen grain landed. In this way, the genetic material of the cell nucleus of both parents is incorporated into the seed. This is important, as it allows the removal of harmful mutations that may accumulate in genetic material over generations.

Organelles harbor their own genome

In addition to the genetic material in the cell nucleus, mitochondria and chloroplasts also contain genetic material. Mitochondria are the engines of cell combustion. Animal and plant cells use them to burn carbohydrates and utilize the released energy for metabolism. Plants also contain chloroplasts. They contain the green pigment chlorophyll, which is the solar power plants of cells. Chloroplasts allow plants to collect solar energy in a process known as photosynthesis to produce carbohydrates.

Mitochondria and chloroplasts have their own genetic material, as they originate from bacteria that were eaten by the ancestors of modern animal and plant cells over a billion years ago. Mitochondria and chloroplasts have created a symbiotic community within the cell, and former roommates are now indispensable to plant survival.

It is known that the genomes of mitochondria and chloroplasts, in contrast to the genetic material in the cell nucleus, are not inherited equally from the father and mother. Both are transmitted almost exclusively by the mother, either because they either do not enter the sperm at all, or their genetic material is dissolved in pollen. If the mitochondria and chloroplasts of the mother and father did not meet, they could not have sex to exchange genetic material. Therefore, deleterious genetic mutations must accumulate over generations and eventually lead to genome collapse.

Scientists have evaluated nearly four million plants

Scientists at the Max Planck Institute for Molecular Plant Physiology have discovered that, contrary to popular belief, tobacco plants can routinely transfer chloroplasts from the parent plant under certain environmental conditions. The researchers first created ab plants that contained antibiotic-resistant chloroplasts. These plants were then exposed to different environmental conditions such as heat, cold, drought and strong light during pollen maturation. Pollen from these plants was used to pollinate unmodified parent plants.

Seeds produced from this cross were grown in culture medium containing the appropriate antibiotic. Since only chloroplasts survive on this medium, cells containing chloroplasts from the parent plant appear green, while plants containing only chloroplasts inherited from the mothers are pale, as these chloroplasts fade due to their sensitivity to antibiotics . Because paternally inherited chloroplasts are so rare, the scientists had to look at nearly four million seedlings to prove that the proportion of paternally inherited chloroplasts was 150 times higher under cold treatment than under normal temperature.

Chloroplast inheritance can be manipulated

After this initial success, the researchers delved into the details: “We know that cold slows the activity of enzymes. We therefore suspect that an enzyme may be involved in blocking chloroplast paternal inheritance,” commented Enrique Gonzalez-Durán, who was also involved in the study. The scientists selectively bred plants with a defective enzyme that normally breaks down the genetic material of chloroplasts during pollen maturation. Plants with a defective enzyme also showed a significant increase in paternal inheritance of chloroplasts. When combining the enzyme defect with cold application during pollen development resulted in a paternal inheritance rate of 2 to 3 percent. “This may not sound like much, but it is huge compared to the 1 in 100,000 chance of this happening under normal conditions. It will be very interesting to see if the chloroplasts inherited from the mother and father actually exchange genetic material with each other,” says Ken Pan Chung. , another author of the study.

The discovery that the heritability of chloroplasts can be controlled by temperature and changes in individual enzymes in a plant opens up entirely new possibilities for plant breeding. “Because it was previously thought that mitochondria and chloroplasts were always inherited together and only from the mother, there was no way to pass on the traits encoded in their genetic material separately. The possibility of chloroplasts also being passed on from the father by placing plants in the cold could open the door to breeding programs. completely new,” explains Ralf Bock, head of the research group.

The reason why mitochondria and chloroplasts are inherited from the mother is still not clear. The fact that this type of inheritance can respond so flexibly to environmental conditions is likely to lead evolutionary biologists to rethink some of their current theories and models. “This also shows how important it is to consider environmental conditions in genetic research. Chloroplasts led us to believe for decades that they lived sexually abstinent, but now we can’t be sure anymore,” says Bock.

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