In most flowering plants, mitochondrial DNA is maternally inherited. In Nicotiana tabacum (tobacco), this maternal inheritance pattern is considered very strict, meaning the father normally does not pass on mitochondrial DNA at all.

This maternal inheritance pattern has important consequences. If a mother plant carries a mutation (a genetic defect) in her mitochondrial DNA, that defect is almost always passed on to all of her offspring. In some cases, these mitochondrial mutations can affect how the plant grows and develops.

One example where mitochondrial defects are especially noticeable is in pollen, the male reproductive cells of plants. If the mitochondria do not work well, pollen may fail to develop properly. This can result in a condition called cytoplasmic male sterility (CMS), where a plant is unable to produce functional pollen.

Mitochondrial inheritance and cytoplasmic male sterility

CMS can actually be useful for plant breeders because it allows an efficient production of hybrid seeds. However, CMS is still a biological defect, as the plant cannot reproduce normally on its own. Since mitochondria are inherited only from the mother, simply crossing a female mitochondrial mutant plant with a healthy male plant does not fix this reproduction defect. Even if the father has perfectly functional mitochondria, they are usually not passed on to the offspring. The defective mitochondria from the mother continue to dominate.

This raises an intriguing question: What if, under certain conditions, the father could pass on mitochondria? If that were possible, could the reproductive defect be corrected? But an even more fundamental question comes first: Is it possible at all to achieve paternal mitochondrial inheritance in tobacco?

Father does contribute, it's just often overlooked

Like mitochondria, plastids in tobacco are generally thought to be inherited maternally. However, when researchers examine a large number of offspring using sensitive methods to detect paternal plastids, they found that the father plant can indeed sometimes pass on plastid DNA. This means paternal inheritance does happen, but it has been difficult to detect because existing methods are not sensitive enough.

To investigate if fathers can also pass on mitochondria, we developed a highly sensitive screening method that can detect mitochondria inherited from the father. Using this approach, we found clear evidence that paternal mitochondria can indeed be transmitted to the next generation. Interestingly, this paternal inheritance happens more often under certain conditions. For example, when we use a cold-stressed tobacco mutant (that lacks the exonuclease DPD1) as the pollen donor, the rate of paternal mitochondrial inheritance can rise to more than seven percent.

Even more remarkably, the mitochondria inherited from the father can fix defects in the maternal mutant mitochondria and restore the plant’s ability to produce pollen, effectively bringing back male fertility.

Left flower – a mutant plant producing nonviable pollen; Right flower – a plant that inherited mitochondria from the father, producing functional pollen and regaining fertility.

Why our findings matter?

Our findings suggest that paternal mitochondrial transmission may be less rare than we previously believed. This has several important implications:

1. It may offer a way to rescue harmful mutations
   If healthy mitochondria from the father can occasionally be transmitted, they could help compensate for defects in the mother’s mitochondrial DNA.

2. It opens the door to mitochondrial “mixing”
   If mitochondria from both parents are present, their genetic material could potentially recombine. This could generate new mitochondrial DNA combinations and influence how mitochondrial genomes evolve over time.

3. It challenges a long-standing assumption about mitochondrial inheritance
   While maternal inheritance remains the dominant rule, it is not as strict as once believed. Even rare exceptions can have major biological and evolutionary consequences.