Paternal Mitochondria Rescuing Plant Fertility

New Study Reshapes Understanding of Mitochondrial Inheritance

To the Point

• Mitochondrial Inheritance: A new study shows that plants can inherit mitochondria from their father, restoring fertility when maternal mitochondria are defective.
• Enhanced Transmission: Paternal inheritance frequency increases significantly under two conditions: enzyme inactivation that degrades mitochondrial DNA and exposure to low temperatures during pollen development.
• Implications for Plant Breeding: This research challenges traditional views on mitochondrial inheritance and opens new opportunities for improving crop varieties through better mitochondrial genome management.

In most plants and animals, including humans, mitochondria are inherited exclusively, or nearly exclusively, from the mother. By contrast, paternal transmission is observed only occasionally, and the mechanisms behind this phenomenon have remained largely unknown.

In a new study researchers established a genetic screening system in tobacco plants that allowed them to detect paternal mitochondrial inheritance. They discovered that paternal transmission is more frequent than previously thought, and found conditions that boost it to even higher levels. Paternal inheritance can rescue plant growth and fertility when maternal mitochondria are dysfunctional.

Curly leaves

To be able to follow mitochondrial inheritance, the researchers developed a genetic screening system using tobacco plants engineered to carry functionally impaired mitochondria with easily recognizable visual growth defects. The engineered plants grew slowly, had curly leaves and developed wrinkled flowers with functional ovaries but sterile pollen. These flowers were then fertilized with pollen from plants carrying healthy mitochondria. While most of the offspring exclusively harbored maternal mitochondria and showed the expected defects, plants carrying paternal mitochondria can be readily identified by their normal growth properties. Molecular analyses and cutting-edge microscopy techniques confirmed the presence of paternal mitochondria and revealed the fate of mitochondria and their genomes during pollen development.

Mitochondria in sperm cells

The team found that paternal transmission occurs at a basal frequency of 0.18 percent, but rises dramatically to over seven percent when two conditions are combined: inactivation of an enzyme that degrades the mitochondrial DNA, and exposure of developing pollen to low temperature. Under these conditions, paternal mitochondria readily enter sperm cells and retain their genome, thus enabling their transmission to the offspring. Remarkably, paternal mitochondria restored normal development and fertility in plants that otherwise inherited defective mitochondria from their mother.

The findings challenge the idea that mitochondrial genomes function as strictly “asexual” genetic systems. If mitochondria from both parents occasionally mix, they can exchange genetic material (referred to as recombination), and create new mitochondrial genetic make-ups. This discovery also opens up new opportunities for plant breeding, particularly with respect to cytoplasmic male sterility, a trait encoded by the mitochondrial genome and widely used to produce hybrid seeds that give rise to high-yielding crop varieties.

“Understanding how mitochondrial inheritance can be controlled gives us powerful new tools for crop breeding,” says Ralph Bock, director at the Max Planck Institute for Molecular Plant Physiology and co-author of the study. “By enabling mitochondria to be transmitted by pollen, we will be able to generate new mitochondrial genomes that can improve stress tolerance, restore fertility, and help develop crops better suited for future environmental challenges.”

Maternal versus paternal transmission

By altering mitochondrial inheritance, it also will be possible to directly compare the pros and cons of maternal versus paternal transmission. In this way, the work brings scientists closer to solving one of biology’s enduring mysteries: why maternal inheritance of mitochondria became dominant in both animals and plants. “This discovery provides us with a new tool to develop better and more resilient crops, and one day, it may explain why we get our mitochondria only from our mothers” says first author Enrique Gonzalez-Duran.

Even under the most favorable conditions identified by the researchers, paternal mitochondria are still only found in a relatively small fraction of the offspring, suggesting that there are additional mechanisms that promote maternal inheritance, which remain to be discovered.

In summary, the study opens new avenues for research into mitochondrial inheritance, and may ultimately contribute to the development of more climate-resilient crops.