UF researcher part of papaya study that sheds light on development of sex chromosomes
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 and 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.