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GAINESVILLE, Fla. — For humans, gender is one of the defining characteristics of life, but for papayas, it’s more like a work in progress.
This tropical fruit crop reproduces sexually, meaning there are male and female papaya trees. But there’s also a third type with the reproductive capacity of both genders. This type is called a hermaphrodite and, unlike male or female plants, it can self-pollinate.
Now, a study involving current University of Florida researcher Jianping Wang helps explain how the plant’s sex chromosomes evolved over time to produce the three genders. Wang was lead author of the paper and performed the work while a postdoctoral fellow with the University of Illinois at Urbana-Champaign.
The findings, published last week by Proceedings of the National Academy of Sciences, shed light on evolutionary processes. The data might also have practical value for papaya growers, who say they get bigger yields and better fruit from hermaphroditic plants.
“In the future, if we understand the process of sex determination clearly, not only can we evaluate young plants before they’re in the ground, and select plants with the gender we want, but also we can identify the sex determination genes and manipulate a pure inbred papaya plant for papaya growers,” said Wang, an agronomy assistant professor with UF’s Institute of Food and Agricultural Sciences.
That approach could be used for other crops that reproduce sexually, she said. For example, asparagus growers prefer to raise male plants.
In the study, Wang and colleagues led an eight-institution team that analyzed genes from sex chromosomes, long strings of DNA sequences that code for anatomical traits we know as gender. The researchers worked with a group of genes in a sex-determination region of the chromosome that controls development of flowers with both male and female characteristics in hermaphrodites, and also a corresponding region from female sex chromosomes. First, they mapped the DNA sequences from both regions of the sex chromosomes, then compared the sequences.
Comparisons revealed that the female sex chromosome region had a shorter DNA sequence – about 3.5 million DNA base pairs, compared with 8.1 million base pairs for the hermaphroditic plant. Many of those extra DNA sequences appear to distinguish the hermaphrodite from the female plant.
This finding supports a hypothesis about the evolution of sex chromosomes: Genders only develop after DNA sequences become altered and a species established two distinct but similar genomes. Later, it’s believed, these fundamental genetic differences become more pronounced and give rise to distinctive sex types.
Since arriving at UF in 2010, Wang has been sequencing genes in bioenergy crops such as energycane, searching for genes that influence the potential value of the plants as feedstocks. Ultimately, she wants to help produce crops with high biomass yields, good disease resistance and chemical profiles well-suited to processing.
Writer: Tom Nordlie, 352-273-3567, firstname.lastname@example.org
Source: Jianping Wang, 352-273-8104, email@example.com
Cutline: Jianping Wang, an agronomy assistant professor with the University of Florida’s Institute of Food and Agricultural Sciences, poses in her lab on the main UF campus — Friday, Aug. 3, 2012. While a postdoctoral associate at the University of Illionois at Urbana-Champaign, Wang was part of a research team that conducted genetic analyses on papaya to shed light on the evolution of the species’ sex chromosomes. The study, published in the journal Proceedings of the National Academy of Sciences, may lead to methods for determining the gender of crop plants before they’re in the ground. For certain crops, including papaya and asparagus, producers prefer to grow plants of one gender. UF/IFAS photo by Tyler L. Jones