- Banyan trees (Ficus microcarpa) have more segmental duplications in its genome which increased the number of genes involved in the synthesis and transport of auxins.
- The levels of auxin in the aerial roots are five times higher than in the leaves of trees with or without aerial roots and this seems to trigger aerial root production.
- Researchers observed that the fig wasps were retaining and preserving genes for odorant receptors that detect the smelly compounds the Banyans fig trees produce. This is an example of coevolution of banyan trees and fig wasps.
Researchers have identified regions in the banyan (Ficus microcarpa) fig’s genome that leads to the development of the unusual aerial roots and enhances its ability to signal wasp pollinator.
A paper describing the study recently appeared in Cell journal. Ray Ming, a plant biology professor at the University of Illinois, Urbana-Champaign led the study with Jin Chen, of the Chinese Academy of Sciences
We know that the banyan fig tree has aerial roots. It also has a unique relationship with a wasp. Wasp has evolved with the banyan tree and is the only insect that can pollinate it.
The team of researchers identified a sex-determining region in a related fig tree, Ficus hispida. F. microcarpa produces aerial roots and bears male and female flowers on the same tree whereas F. hispida have distinct male and female trees and have no aerial roots.
“Understanding the evolutionary history of Ficus species and their wasp pollinators is important because their ability to produce large fruits in a variety of habitats makes them a keystone species in most tropical forests,” said Ray Ming.
Another scientific challenge is the relationship between figs and wasps. The body shapes and sizes of the wasps correspond exactly to those of the fig fruits, and each species of fig produces a unique perfume to attract its specific wasp pollinator.
The team analyzed the genomes of the two fig species along with that of a wasp that pollinates the banyan tree to understand this evolutionary developments.
The team sequenced the trees’ genomes and found more segmental duplications in the genome of the banyan tree than in F. hispida, the fig without the aerial roots. They found that these duplicated regions account for about 27% of the genome.
The duplications increased the number of genes involved in the synthesis and transport of auxins, a class of hormones that promote plant growth.
“The levels of auxin in the aerial roots are five times higher than in the leaves of trees with or without aerial roots,” Ming said. These higher auxin levels seems to trigger aerial root production. The duplicated regions also include genes that code for a light receptor that accelerates auxin production.
On studying and comparing the genome of the fig wasp with those of other related wasps, the researchers observed that the wasps were retaining and preserving genes for odorant receptors that detect the smelly compounds the fig trees produce. These genomic signatures are a signal of coevolution between the fig trees and the wasps, the researchers report.
Ming and his colleagues also discovered a Y chromosome-specific gene that is expressed only in male plants of F. hispida and three other fig species that produce separate male and female plants, a condition known as dioecy.
“This gene had been duplicated twice in the dioecious genomes, giving the plants three copies of the gene. But Ficus species that have male and female flowers together on one plant have only one copy of this gene,” Ming said. “This strongly suggests that this gene is a dominant factor affecting sex determination.”
Xingtan Zhang, Gang Wang, Shengcheng Zhang, Shuai Chen, Yibin Wang, Ping Wen, Xiaokai Ma, Yan Shi, Rui Qi, Yang Yang, Zhenyang Liao, Jing Lin, Jishan Lin, Xiuming Xu, Xuequn Chen, Xindan Xu, Fang Deng, Lihua Zhao, Yi-lun Lee, Rong Wang, Xiao-Yong Chen, Yann-rong Lin, Jisen Zhang, Haibao Tang, Jin Chen, Ray Ming. Genomes of the Banyan Tree and Pollinator Wasp Provide Insights into Fig-Wasp Coevolution. Cell, 2020; DOI: 10.1016/j.cell.2020.09.043
Press Release: University of Illinois at Urbana-Champaign