proportion of female plants and significantly boost- ing the yield of fiber, oil, and protein. This ground- breaking research has the potential to revolutionize hemp cultivation, making it a more sustainable and profitable crop for farmers while providing consum- ers with high-quality, eco-friendly products.
Nicole Stark and Sarah Carey, PhD, analyzing sex chromosome characterization data.
TRACING SEX CHROMOSOME EVOLUTION TO UNDERSTAND PLANT REPRODUCTION
Male Amborella flower
Thanks to support from an NSF CAREER grant , Harkess and his lab are characterizing sex chro- mosomes and sex-determining genes across every order of flowering plants, the largest genomic sampling of dioecious plant species to date. To help them achieve that monumental goal, the lab devel- oped a pipeline called Cytogenetics-by-Sequencing (CBS) to more easily and inexpensively identify and characterize sex chromosomes in plants. So far, they have successfully used the CBS pipeline to dis- cover new sex chromosomes in nearly 30 dioecious plant and animal species. The immense amount of data produced during this study will serve as an invaluable resource for plant breeding. Harkess’s team plans to use the information to identify new genes that control sex in plants and engineer artificial sex chromosomes to genetically modify hermaphroditic crops. This could revolutionize agriculture by giving farmers unprec- edented control over plant sex determination, allow- ing them to cultivate only desired sexes, accelerate breeding programs, reduce unwanted pollination, and adapt plants to changing environments. Industrial hemp is a specific crop that will benefit from the Harkess lab’s work. This versatile crop has a rich history and has been used for centu- ries for a wide variety of purposes, including fiber, grain, and oil. Female hemp plants are particularly valuable due to their higher biomass production and exclusive ability to yield seeds rich in beneficial lipids and proteins. Through a USDA-NIFA-funded grant , Harkess and his lab, along with collaborators at New West Genetics, will interrogate the hemp sex chromosomes to identify the master sex determina- tion genes in hemp. Manipulating these genes could allow for precise control of plant sex, increasing the
Studying sex-determination genes can help us understand how plant reproduction has evolved over time. Flowering plants, which the Harkess lab studies extensively, have evolved dioecy independently hundreds of times, making them an ideal model for studying the evolution of plant reproductive systems. Amborella trichopoda , a fascinating dioecious plant, offers a glimpse into the early evolution of flowering plants. As the only living species in the sister lineage to all other flower- ing plants, it offers a valuable reference point for studying the evolution of sex determination. Comparing Amborella ’s genetics to other flowering plants can help researchers trace the evolution of dioecy and other reproductive strategies. In 2024, the Harkess lab published the most complete and accurate Amborella genome to date in Nature Plants 1 . Using advanced sequencing techniques, the team assembled highly contiguous genome sequences, including the Amborella Z and W sex chromosomes, which are historically difficult to assemble. The team determined that Amborella ’s sex chromosomes evolved after it split off from other living flowering plants. This allowed them to examine the early stages of sex chromosome evolution and identify potential sex-determining genes. Understanding the genetic mechanisms that led to dioecy in Amborella could help develop controllable sex determination systems in agri- cultural crops. This research provides a strong foundation for studying sex chromosome evolution in all flowering plants. ■
Read this Everyday DNA blog article to learn more.
RESEARCH REPORT 2023-2024
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