New research! Chinese scientists discovered the "control switch" of plant life cycle

The Cruciferae family is one of the most prosperous plant families, and many crops that can be seen in daily life come from this family, such as rapeseed, cabbage, broccoli, etc.

On May 28, 2024, the international academic journal Cell published online a research paper titled "Reciprocal conversion between annual and polycarpic perennial flowering behavior in the Brassicaceae" by Wang Jiawei's research team from the Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences.

The researchers have successfully identified three key genes in the Cruciferae family that determine the perennial nature of plants. By knocking out these three genes in perennial plants or transferring these three perennial genes into annual plants, the Cruciferae family can achieve mutual conversion between perennial and annual life habits.

Only three genes need to be changed to achieve the conversion of annual and perennial life habits of cruciferous plants. Image source: Reference [1]

What are perennial crops?

Plants can be simply divided into annuals, biennials and perennials based on the time it takes to complete a life cycle. Annual plants consume a lot of energy to produce seeds after flowering until the entire plant dries up and dies.

Most perennial plants will consume energy in moderation after flowering, thereby retaining some energy and new shoots, and then enter a vegetative growth state (i.e. growing new leaves and thriving development), and do this year after year, achieving longevity in the cycle of flowering and vegetative growth.

From the small grass that "withers and grows again every year" to the big tree with luxuriant branches and leaves, the fact that plants have diverse living habits is well known to everyone, but what is the "switch" that really determines the lifespan of a plant is not very clear.

From the application perspective, perennial crops are an effective supplement to traditional annual crops. They have the characteristics of "one sowing, multiple harvests", avoiding repeated tillage, which not only saves manpower and machinery costs, but also protects soil structure.

In addition, the well-developed root system of perennial crops can ensure high water and fertilizer utilization, reduce soil loss, and fix carbon in the atmosphere in the soil layer. It is an important strategic reserve for China to promote sustainable agricultural development and respond to future climate change.

Where did we find the perennial gene?

How to find the gene that determines the perenniality of plants? There is a logically simple research strategy. First, find a pair of annual and perennial plants that can be hybridized. According to common sense in genetics, their offspring will be both annual and perennial. By analyzing the genotype and phenotype of the offspring, the gene that determines the perenniality of plants can be found.

The above research strategy sounds very simple, but few other laboratories around the world have tried it. The reason is first of all technical limitations . In the past decade, genome sequencing technology and gene editing technology have developed rapidly, allowing more and more plants to be used for molecular genetic research, which was difficult to achieve before.

The more important reason is that the actual operation is difficult and requires a lot of labor. Annual and perennial plants are often classified as different species and have reproductive isolation. The probability of distant hybridization across species producing normal fertile offspring is extremely low, so if you want to succeed, you can only make more attempts.

To this end, as early as ten years ago, Professor Wang Jiawei's team began collecting Cruciferae materials, covering hundreds of plant materials including the genera Sumeruina, Saccharina, Cardamine, and Araucaria.

The team first investigated the living habits (annual or perennial) of the collected plants, then evaluated the genome size, combined morphological characteristics and molecular markers to assess genetic relationships, and preliminarily screened the "annual-perennial" plant combinations that might be successful.

What followed was a long series of attempts, and finally two pairs of hybrid combinations that could produce offspring were obtained, namely Crucihimalaya himalaica and Crucihimalaya wallichii of the genus Crucihimalaya; and Erysimum nevadense and Erysimum cheiranthoides of the genus Erysimum.

Perennial plants have a long life cycle, and often the experimental results of the seedlings planted today will not be available until next year. During this period, the plants may be stressed by factors such as drought and pests, which will affect the experimental data, so they need to be taken care of continuously and carefully. From a rigorous perspective, researchers do not want the plants to be stressed by factors such as drought and pests, which will affect the experimental data. This also means that researchers have to give up the opportunity to take a long vacation, and plants will not stop growing because of people's vacations.

Perennial plants, especially Himalayan mustard, are native to the Qinghai-Tibet Plateau and need to undergo five months of low-temperature treatment (simulating winter conditions) before they can bloom. In artificially simulated winter cold storage, aging leaves are prone to mold and rot and need to be cleaned regularly.

In order to prevent the plants from being affected by temperature fluctuations, these operations are often carried out in a cold storage. In summer, scientific researchers wearing short-sleeved shirts and shorts put on down jackets outside the door and enter the cold storage to work.

Let's briefly review the timeline of the project. The project started in 2014, the first annual/perennial hybrid combination was obtained in 2017, the second hybrid combination was obtained in 2018, and all the mutant materials needed for the experiment were obtained in 2022. Most of the data in the published paper were actually completed in the past three years. However, the above efforts that cannot be shown in the paper are the cornerstone of it.

Conclusion of the work

Through genetic positioning, the researchers found three key genes that determine the life habits of plants in both the Brassica and Sacchariflora genera, namely FLC, FLM and MAF. The three belong to a class of closely related flowering inhibition genes.

The researchers used gene editing technology to knock out the FLC, FLM and MAF genes of the perennial Himalayan mustard one by one, and found that the loss of these genes one by one would cause the plant to change from perennial to biennial, and then further to annual.

Combining transcriptome and epigenomic data, the researchers summarized the core molecular mechanisms that determine the perennial flowering strategy of plants. The FLC, FLM, and MAF genes of perennial plants inhibit flowering before winter. Low temperatures in winter silence the expression of these genes, allowing plants to bloom in spring. As the temperature rises, genes such as FLC will be reactivated, causing the plants to end their flowering period and return to a state of vegetative growth, so that the flowers are similar year after year.

The researchers then transferred the perennial FLC, FLM and MAF genes into annual (including winter annual) Saccharum officinale, Arabidopsis thaliana and rapeseed, and successfully converted the above plants to perennial habits.

Future Outlook

Ideally, perfect scientific research work needs to include two major elements: interesting scientific stories and practical application value.

In summary, there is still a long way to go to create applicable cruciferous perennial crops based on the existing theoretical foundation. Can rapeseed that can grow perennially under greenhouse conditions maintain perenniality in the more complex and changeable environment of the field? When perennial plants bloom and bear fruit, part of the energy is given to seeds and part of the energy is used to maintain their own survival. Does this mean that the yield of perennial crops will be lower than that of traditional crops? Can crops achieve a perfect balance between yield and maintaining their own perenniality through targeted molecular design? These scientific problems that have the potential to be applied to actual production will be the focus of future work.

References

[1] Zhai D, Zhang LY, Li LZ, et al. (2024). “Reciprocal conversion between annual and polycarpic perennial flowering behavior in the Brassicaceae.” Cell

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Produced by | Science Popularization China

Author: Wang Jiawei and Zhai Dong (Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences)

Producer｜China Science Expo

Editor: Yang Yaping

Proofread by Xu Lailinlin