hajime.sakai@napigen.com

Cytoplasmic male sterility (CMS) has become the genetic foundation of creating F1 hybrid seed to unlock unprecedented yield potentials in many crop plants. Wheat is a prime example of a crop that can benefit from hybridization. It has been reported that yield gains of 15% or more could be achieved in F1 hybrids of various wheat lines. Encouraged by this promise, private and public organizations have invested significant efforts over past decades to turn the biological gains of hybrid vigor into agricultural advantages.

While the efforts continue, two challenges remain recalcitrant. One is the male sterility of female and the other is the pollen shedding of male plants. The former is perhaps most critical for large-scale hybrid seed productions. So far, the source of male sterility in industrial operations has been limited to a few CMS lines that were originated from crosses of modern wheat plants with less cultivated, often wild, wheat species as cytoplasmic donors.

These alloplasmic plants tended to have unstable mitochondrial genomes, producing novel DNA molecules through complex recombination. A few of the rearranged mitochondrial DNAs resulted in CMS genes. However, most of CMS plants exhibit conditional male sterility. Additionally, due to incompatibility between the nuclear and cytoplasmic genomes, many of the alloplasmic plants are agronomically inferior over cultivated wheat, making their industrial use challenging.

To create better CMS plants, it is highly desirable to have molecular tools to engineer mitochondrial genomes to precisely introduce the best CMS genes into the wheat germplasm pool. Motivated by the potential benefits to our society, we founded NAPIGEN to develop such tools for mitochondrial gene editing.

Our success in single cell organisms, yeast and alga, has now been replicated with plant mitochondrial genomes. We have demonstrated the integration of exogenous genes into specific sites of the rice mitochondrial genome, leading to proper gene expression. We are introducing CMS genes into rice and wheat mitochondrial genomes to enable the creation of customized CMS plants in elite crop backgrounds.

We expect this will help circumvent the alloplasmic and phenotypic expression problems of existing CMS plants. Our technology will improve current hybrid wheat production systems and facilitate robust yield gains.