Salk News
Salk researchers discover that miniature aquatic plant provides insight into genome design principles that could enable development of next-generation crops.
LA JOLLA—Wolffia, also known as duckweed, is the fastest-growing plant known, but the genetics underlying this strange little plant’s success have long been a mystery to scientists. Now, thanks to advances in genome sequencing, researchers are learning what makes this plant unique—and, in the process, discovering some fundamental principles of plant biology and growth.
A multi-investigator effort led by scientists from the Salk Institute is reporting new findings about the plant’s genome that explain how it’s able to grow so fast. The research, published in the February 2021 issue of Genome Research, will help scientists to understand how plants make trade-offs between growth and other functions, such as putting down roots and defending themselves from pests. This research has implications for designing entirely new plants that are optimized for specific functions, such as increased carbon storage to help address climate change.
“A lot of advancement in science has been made thanks to organisms that are really simple, like yeast, bacteria and worms,” says Todd Michael, first author of the paper and a research professor in Salk’s Plant Molecular and Cellular Biology Laboratory. “The idea here is that we can use an absolutely minimal plant like Wolffia to understand the fundamental workings of what makes a plant a plant.”
Wolffia, which is found growing in fresh water on every continent except Antarctica, looks like tiny floating green seeds, with each plant only the size of a pinhead. It has no roots and only a single fused stem-leaf structure called a frond. It reproduces similar to yeast, when a daughter plant buds off from the mother. With a doubling time of as little as a day, some experts believe Wolffia could become an important source of protein for feeding Earth’s growing population. (It’s already eaten in parts of Southeast Asia, where it’s known as khai-nam, which translates as “water eggs.”)
To understand what adaptations in Wolffia’s genome account for its rapid growth, the researchers grew the plants under light/dark cycles, then analyzed them to determine which genes were active at different times of the day. (Most plants’ growth is regulated by the light and dark cycle, with the majority of growth taking place in the morning.)
“Surprisingly, Wolffia only has half the number of genes that are regulated by light/dark cycles compared to other plants,” Michael says. “We think this is why it grows so fast. It doesn’t have the regulations that limit when it can grow.”
The researchers also found that genes associated with other important elements of behavior in plants, such as defense mechanisms and root growth, are not present. “This plant has shed most of the genes that it doesn’t need,” Michael adds. “It seems to have evolved to focus only on uncontrolled, fast growth.”
“Data about the Wolffia genome can provide important insight into the interplay between how plants develop their body plan and how they grow,” says HHMI Investigator and Professor Joseph Ecker, who is also director of Salk’s Genomic Analysis Laboratory and a coauthor of the paper. “This plant holds promise for becoming a new lab model for studying the central characteristics of plant behavior, including how genes contribute to different biological activities.”
One focus of Michael’s lab is learning how to develop new plants from the ground up, so that they can be optimized for certain behaviors. The current study expands knowledge of basic plant biology as well as offers the potential for improving crops and agriculture. By making plants better able to store carbon from the atmosphere in their roots, an approach pioneered by Salk’s Harnessing Plants Initiative, scientists can optimize plants to help address the threat of climate change.
Michael plans to continue studying Wolffia to learn more about the genomic architecture of plant development by using this simplified plant to understand the networks that control fate.
Other authors on the study were Nolan Hartwick, Florian Jupe and Justin P. Sandoval of Salk; Evan Ernst and Robert A. Martienssen of Cold Spring Harbor Laboratory; Philomena Chu, Sarah Gilbert, and Eric Lam of Rutgers, The State University of New Jersey; Douglas Bryant and Todd C. Mockler of Donald Danforth Plant Science Center; Stefan Ortleb, Joerg Fuchs, and Ljudmylla Borisjuk of Leibniz Institute of Plant Genetics and Crop Plant Research in Germany; Erin L. Baggs and Ksenia V. Krasileva of the University of California, Berkeley; K. Sowjanya Sree of Central University of Kerala, in India; and Klaus J. Appenroth of Friedrich Schiller University of Jena, in Germany.
This work was funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research program. It was also supported by a grant from the Hatch project from the New Jersey Agricultural Experiment Station at Rutgers University and the Howard Hughes Medical Institute.
DOI: 10.1101/gr.266429.120
I'm Todd Michael, a research professor in Salk's Plant Molecular and Cellular Biology Laboratory and the first author of the paper published in the February 2021 issue of Genome Research. My expertise lies in the field of plant biology, particularly in understanding the genetic makeup and growth mechanisms of plants. The research conducted by a multi-investigator team, with me at the forefront, focused on unraveling the mysteries behind the rapid growth of Wolffia, also known as duckweed, which is considered the fastest-growing plant.
The study utilized cutting-edge genome sequencing techniques to delve into the genetic architecture of Wolffia, shedding light on how this tiny aquatic plant achieves its remarkable growth. The findings have broader implications for our understanding of fundamental principles in plant biology and growth, with potential applications in the development of next-generation crops optimized for specific functions.
Wolffia's unique characteristics, such as its minuscule size, absence of roots, and rapid reproduction akin to yeast, make it an intriguing subject for scientific exploration. By growing the plants under light/dark cycles and analyzing gene activity at different times of the day, we uncovered that Wolffia exhibits only half the number of genes regulated by light/dark cycles compared to other plants. This lack of regulatory constraints is believed to contribute to its exceptional growth rate.
Moreover, the study revealed that Wolffia has streamlined its genome by discarding unnecessary genes associated with defense mechanisms and root growth. This suggests that the plant has evolved to prioritize uncontrolled, fast growth. The implications of this research extend beyond understanding Wolffia's genome; it opens up possibilities for designing entirely new plants tailored for specific purposes, including increased carbon storage to mitigate climate change.
Collaborating with experts from various institutions, including Cold Spring Harbor Laboratory, Rutgers University, Donald Danforth Plant Science Center, and others, our work represents a significant advancement in plant biology. The genomic insights gained from Wolffia not only contribute to our understanding of plant development but also hold promise for improving crops and agriculture.
Continuing our exploration, my lab aims to delve deeper into Wolffia's genomic architecture to unravel the networks controlling plant development. This research contributes to the broader scientific community's knowledge and may pave the way for using Wolffia as a new lab model for studying fundamental aspects of plant behavior. The research was made possible by the support of institutions such as the US Department of Energy, the Howard Hughes Medical Institute, and the New Jersey Agricultural Experiment Station at Rutgers University.
