An international team of researchers has generated and analyzed draft reference genomes of Wolffia australiana, which has the smallest genome size in its genus. The findings 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.
Wolffia is a genus of over ten species found growing in fresh water on every continent except Antarctica.
Commonly called watermeal or duckweed, it includes the fastest-growing and smallest flowering plants on Earth.
Wolffia species look like tiny floating green seeds, with each plant only the size of a pinhead.
They have no roots and only a single fused stem-leaf structure called a frond. They reproduce 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.
“A lot of advancement in science has been made thanks to organisms that are really simple, like yeast, bacteria and worms,” said Professor Todd Michael, a researcher in the Plant Molecular and Cellular Biology Laboratory at the Salk Institute for Biological Studies.
“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.”
To understand what adaptations in Wolffia’s genome account for its rapid growth, Professor Michael and colleagues grew the Wolffia australiana plants under light/dark cycles, then analyzed them to determine which genes were active at different times of the day.
“Surprisingly, Wolffia only has half the number of genes that are regulated by light/dark cycles compared to other plants,” Professor Michael said.
“We think this is why it grows so fast. It doesn’t have the regulations that limit when it can grow.”
The scientists found that genes associated with other important elements of behavior in plants, such as defense mechanisms and root growth, are not present in Wolffia australiana.
“This plant has shed most of the genes that it doesn’t need. It seems to have evolved to focus only on uncontrolled, fast growth,” Professor Michael said.
“Data about the Wolffia australiana genome can provide important insight into the interplay between how plants develop their body plan and how they grow,” said Professor Joseph Ecker, a researcher at the Howard Hughes Medical Institute and director of Salk’s Genomic Analysis Laboratory.
“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.”
The results appear in the journal Genome Research.
Todd P. Michael et al. Genome and time-of-day transcriptome of Wolffia australiana link morphological minimization with gene loss and less growth control. Genome Research, published online December 23, 2020; doi: 10.1101/gr.266429.120