Exploring the Inevitable Link between Pollen Absence and Seed Production

Researchers at North Carolina State University have achieved the successful transfer of a crucial gene from one section of a plant cell to another, resulting in tobacco plants that grow normally but lack both pollen and viable seeds. This breakthrough has significant implications for enhancing crop productivity through improved hybrid seed production and introducing seedlessness into fruit species that lack this desirable trait, such as raspberries, blackberries, or muscadine grapes.

The researchers initiated their work within the energy-producing portion of plant cells, the mitochondria. In plants, disruptions in the mitochondrial genome can lead to the inability to produce pollen, a characteristic referred to as cytoplasmic male sterility (CMS). CMS has been effectively utilized to generate high-yielding hybrid seeds in many important crops. However, naturally occurring CMS-based systems suitable for large-scale hybrid seed production are limited.

In their proof-of-concept study, the North Carolina State University researchers, collaborating with colleagues from Precision BioSciences and Elo Life Systems, employed an innovative approach to investigate whether they could induce the CMS trait in tobacco, a frequently used model plant species in botanical research.

Initially, the researchers relocated a critical mitochondrial gene called atp1 to the plant cell nucleus, placing it under the regulatory control of a promoter that they predicted would enable the transferred atp1 gene to be expressed in all plant cells except those responsible for pollen production. Subsequently, they used genome editing techniques to permanently remove the native atp1 gene from the mitochondria. Their approach yielded positive results.

Ralph Dewey, the Philip Morris Professor of Crop Science at NC State and the corresponding author of the research paper, remarked, “The outcomes surpassed our expectations. The plants exhibited normal growth until they reached the flowering stage, at which point they failed to produce pollen because the transferred atp1 gene was no longer expressed. Importantly, since the original atp1 gene was eliminated from the mitochondrial genome, the trait will be inherited maternally, a crucial consideration for large-scale hybrid seed production.”

However, the technique did not only affect pollen production. When cross-fertilized with pollen from neighboring normal plants, the tobacco plants unexpectedly produced small, hollow seeds, resembling the “seedless” fruits found in popular varieties like watermelons and grapes. Dewey explained, “This occurred because the selected promoter not only failed to express during pollen formation but also during early seed development.”

Dewey’s team is currently working to separate these results, enabling researchers to achieve either pollen infertility or the seedless trait individually, rather than both simultaneously.

Additionally, Dewey emphasized that these findings are not limited to tobacco plants. The next phase of experiments will involve testing the seedless trait in tomatoes, which are closely related to tobacco. They will also assess their innovative CMS trait in a grain crop, such as rice, to gauge its effectiveness in crops where hybrid seed production plays a crucial role in achieving maximum yields. Dewey stated, “Considering how the system operates, there’s no reason to believe that we couldn’t effectively apply the technology to other plant species.”

This groundbreaking study is featured in Frontiers in Plant Science.

Source: North Carolina State University

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