In Chinese folklore, there's a saying: "When bamboo blooms, disaster looms." It suggests that when bamboo flowers, it signals imminent misfortune. From a scientific standpoint, this folklore is easily debunked.
Bamboo can be categorized into woody and herbaceous types, with only the woody type perishing after flowering. Woody bamboos have tall stems, high lignification levels, and can grow nutritionally for decades, even up to 120 years, before flowering and dying. In contrast, herbaceous bamboos are typically only a few tens of centimeters tall, with low lignification levels, and flower and fruit annually like other grasses.
What scientific principles underlie the unique traits of woody bamboos? A recent study led by Dr. Li Dezhu and his team at the Kunming Institute of Botany, Chinese Academy of Sciences, reveals that "subgenome dominance transfer" occurred during ancient hybridization events among diploid ancestors of woody bamboos, leading to the evolution of their unique traits.
The findings of this study were recently published online in Nature Genetics. This conclusion provides multiple lines of genomic evidence for understanding the diversification and origin of unique traits in bamboo species.
In the study of plant evolutionary history, polyploidization, or whole-genome duplication, has always been a hotspot of scientific inquiry. Woody bamboos, including tetraploid temperate woody clades, neotropical woody clades, and hexaploid old tropical woody clades, comprise about 1,576 species, accounting for 92.6% of the total species diversity within the bamboo subfamily, while the herbaceous clades, primarily diploids, consist of only about 126 species.
The research team has provided a fascinating glimpse into the genomic colinearity between two types of herbaceous bamboos and three representatives each from three woody bamboo lineages (a), and the striking contrast in plant stature between the giant bamboo of the Paleotropics (b) and a representative of the herbaceous lineage (c). (Image courtesy of the research team)
Scientists explain that the genetic mechanisms behind how different subgenomes interact after bamboo polyploidization, and how these interactions affect the species diversity of bamboos, remain elusive.
In their latest study, published in a prestigious journal, the team, leveraging the national infrastructure of the Southwest China Wildlife Germplasm Resources Bank, has successfully acquired chromosome-level genomes of two herbaceous bamboos and three representatives each from temperate, Neotropical, and Paleotropical woody bamboo lineages. They also sequenced 476 transcriptome datasets covering various tissues and developmental stages of bamboos.
Initially, they proposed a network evolution route of hybridization and polyploidization in woody bamboos and hypothesized that the polyploidization in these plants is related to the development of their adaptive traits.
Through comprehensive analysis, the team identified four subgenomes, A, B, C, and D, in woody bamboos and further unveiled ancient hybridization events among the diploid ancestors of woody bamboos.
They revealed that the A and D subgenomes were formed by early hybridization between the B and C subgenomes, with a gene introgression event from the A subgenome into an ancestor of the herbaceous bamboos occurring 22 million years ago.
The researchers observed independent origins of subgenome dominance in two tetraploid lineages across various aspects, including genome size, loss of duplicate genes, repetitive sequences, methylation, and chromosomal structural variations, with the C subgenome showing dominance in both. Moreover, in the hexaploid lineage, subgenome dominance was more dynamic and diverse, showing a transition trend from the C subgenome to the A subgenome.
The scientists highlight that this is the first report of a potential subgenome dominance shift phenomenon in polyploid plant groups, offering a fresh direction for understanding the evolutionary mechanisms of polyploid plants.
Bamboo Subfamily's Diploid Ancestors and the Origins and Duplication Model of Three Woody Lineages. Image courtesy of the research team.
Researchers from the Kunming Institute of Botany, including Pengfei Ma, Yunlong Liu, and Dr. Cen Guo (currently at the Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences), Dr. Guihua Jin, and Zhenhua Guo, served as co-first authors of the paper, with De-Zhu Li as the corresponding author.
Related paper link: https://doi.org/10.1038/s41588-024-01683-0
