A recent analysis of the sunflower family tree used genome skimming to expand the number of species examined, uncovering the independent evolution of flower symmetry, known as convergent evolution, among the various members of this expansive plant family. Led by a Penn State biologist, the research team was able to clarify more of the intricate branches of the family tree, offering insight into the evolution of the sunflower family.
The findings of the study, which was published in the journal Plant Communication, may assist in the identification of beneficial traits for the selective breeding of plants with more desirable features, according to researchers. The study detailed the analysis and results of the research. “Convergent evolution refers to the independent development of what appears to be the same characteristic in different species, such as wings in birds and bats,” explained Hong Ma, leader of the study and professor of biology at Penn State’s Eberly College of Science.
research team members stated that it can be challenging to determine the degree of relatedness between two species by comparing their characteristics. Therefore, having a detailed family tree based on DNA sequences is crucial for understanding the evolution of these traits.
For instance, the sunflower head is made up of multiple smaller flowers, creating a composite structure. Although the head is typically radially symmetrical, with the ability to be divided into two equal halves in various directions, the individual flowers may exhibit different forms of symmetry. The recent study revealed that some flowers display bilateral symmetry, where only one line can divide the flower into identical halves.The splitting of the flower into two equal halves has occurred multiple times independently in sunflowers, and has evolved and been lost throughout their evolutionary history. The researchers discovered that this convergent evolution is likely connected to changes in the number of copies and the patterns of expression of the floral regulatory gene, CYC2.
Recently, many family trees for a group of related species have been constructed by extensively using transcriptomes, which are the genetic sequences of essentially all of the genes expressed by a species, the researchers explained. Transcriptomes are easier to obtain than high-quality whole-genome sequences for a species but are still difficult to acquire.The process of preparing fresh plant samples for genome sequences can be difficult and costly. To compare a larger number of species, the team decided to use low-coverage genome sequences, which are produced through a process called genome skimming and are relatively inexpensive and easy to prepare, even from dried plant samples.
Ma explained, “In order to obtain an accurate whole-genome sequence for a species, each letter of its DNA alphabet must be read multiple times to minimize errors. However, for the purpose of building a family tree, we found that lower coverage genome sequences can be sufficient. This allowed us to increase the number of species available for comparison.”Our analysis of species allowed us to better understand the finer branches on the sunflower family tree. The team utilized a combination of publicly available and newly generated transcriptomes, as well as a large number of newly obtained skimmed genomes, totaling 706 species from 16 subfamilies, 41 tribes, and 144 subtribe-level groups in the sunflower family. These subfamilies, tribes, and subtribes are major subdivisions that contain one or more genera, which is the level of classification above the species.The sunflower family tree’s relationships have been established by Ma, showing the connections between subfamilies and tribes, which are like the main branches of a tree. With a larger sample size, the team was able to resolve more of the smaller branches and twigs at the subtribe and genus level. This higher-resolution tree allowed them to reconstruct the evolution of traits like flower symmetry, indicating that bilateral symmetry evolved independently many times. Additionally, the team studied the molecular evolution of genes involved in flower development among sunflowers, finding that one of these genes, CYC2, had…Multiple copies of CYC2 gene in the genomes of each species suggest that it may play a role in the convergent evolution of bilaterally symmetric flowers. The team conducted experiments to measure CYC2 gene expression in different types of symmetrical flowers to further test this hypothesis.
According to Ma, “Our analysis indicates a strong correlation between CYC2 expression and flower symmetry, implying that variations in the usage of these genes in different sunflower species may be responsible for the observed convergent evolution in the family.”One of the two largest families of flowering plants, with over 28,000 species, contains many economically important agricultural and horticultural species. Understanding the relationships between these species helps us determine how and when their characteristics evolved. This knowledge could also be used to identify useful traits that could be bred into domesticated species from closely related wild ones.”
In addition to Ma, the research team includes Guojin Zhang at Penn State; Junbo Yang, Jie Cai, Zhi-Rong Zhang and Lian-Ming Gao at the Kunming Institute of Botany in Kunming, China; Caifei Zhang at the Wuhan Botanical Garden andThe research was conducted by the Sino-Africa Joint Research Centre in Wuhan, China; Bohan Jiao and Tiangang Gao at the State Key Laboratory of Plant Diversity and Specialty Crops in Beijing, China; and Jose L. Panero at the University of Texas, Austin.
Funding for this research was provided by the Eberly College of Science and the Huck Institutes of the Life Sciences at Penn State, the Strategic Priority Research Program of the Chinese Academy of Sciences, the Large-scale Scientific Facilities of the Chinese Academy of Sciences, and the National Natural Science Foundation of China.
Journal Reference:
- GuojiIn a study by Zhang, Yang, Zhang, Jiao, Panero, Cai, Zhang, Gao, Gao, and Ma, titled “Nuclear phylogenomics of Asteraceae with increased sampling provides new insights into convergent morphological and molecular evolution” published in Plant Communications in 2024, the researchers present their findings. The study’s DOI is 10.1016/j.xplc.2024.100851.