Plants Get Jetlag Too: A Play On Flowering Time
By Patrice A. Salomé
The ephemeral beauty of flowers
Cherry blossoms mark the beginning of Spring, and appear every year as daylight increases. But plants do not have access to a calendar, do they?
Actually, they do have something that fits the bill, called the circadian clock. It can measure how long days are, whether they are getting shorter or longer, and even what time of day it is. You have one too: it lets you know when you should eat and go to sleep. And you can blame it for jetlag when you travel.
A new study by Yong Ding and colleagues (2017) adds a new cog in the time machine that plants use to know when to flower.
When should a plant flower and produce seeds?
Of course, not all plants flower alongside cherry blossoms. Some plants will flower when days become shorter in late Fall, for example soybeans and Poinsettias, while other will flower under longer days only, like peas and wheat.
When they are of age, plants need to decide when to flower and produce seeds to guarantee reproductive success and to start the next generation. Plants do not wait for parental consent, a wedding, or job security, all aspects you might consider before becoming parents yourselves. They just need the right combination of temperature and daylength, to ensure their progeny will not be left out in the cold — often literally.
Imagine that a plant blooms in late spring. In a hot climate, this could mean the death of its progeny due to lack of water during hot and dry summers. Same thing for seeds produced late in the Fall, before cold winters: the progeny will be exposed to frost and freezing temperatures, and may not survive until spring.
CONSTANS: master switch in flowering initiation
You can imagine how important the decision to flower is to a plant; and to us, since we eat what emerges from these flowers, in the form of fruits, vegetables and seeds.
At the heart of a plant’s decision to flower is the gene CONSTANS (CO). Its product accumulates under flowering-promoting conditions, and its levels are modulated by multiple factors (Hayama and Coupland, 2004). In this article, Su and colleagues (2017) describe a new level of modulation of CO levels, and it involves a group of proteins called histones.
Histones are spools for the DNA in our chromosomes
Chromosomes are very much like a spool of yarn, with histones acting as the spool, and DNA wrapping itself around them; very tightly. For scale, the DNA in our cells would stretch to a length of over 6 feet, but histones allow DNA to pack itself neatly into a space smaller than a hair’s width.
To get to the center of the DNA spool and find genes whose products are needed for cells to function, the cellular machinery relies on decorations on histones to be guided to the right neighborhood, just like street signs in our cities. These decorations are added onto histones by a set of enzymes. Su and colleagues found that a type of enzyme, a kinase called MUT9P-LIKE KINASE or MLK4 for short, was responsible for targeting a single amino acid on histones near a gene that affects the expression of CO. The loss of this specific modification decreases the amount of active CO and causes plants to make more leaves and delay the formation of flowers and seeds.
Flowering time and crop harvests: a look to the future
Many crops have been selected by farmers over the past 10,000 years for relative insensitivity to daylength to extend harvesting period throughout the year, as well as conquer higher latitudes.
These results bring us closer to understanding how and when plants decide to stop making leaves and instead produce flowers and seeds, and may help us to breed or engineer crops that have more optimal flowering times for the locations they are grown, as farmers and plant biologists try to find new ways to produce more food for more people on the same amount of arable land.
Patrice A. Salomé
Department of Chemistry and Biochemistry
University of California, Los Angeles
ORCID: 0000–0003–4452–9064
Read the research paper on which this story is based:
Su, Y., Wang, S., Zhang, F., Zheng, H., Liu, Y., Huang, T., and Ding, Y. (2017). Phosphorylation of Arabidopsis histone H2A serine 95: a plant-specific mark involved in flowering time and H2A.Z deposition. Plant Cell published August 8, 2017. doi/10.1105/tpc.17.00266
OTHER CITED REFERENCES
Hayama, R., and Coupland, G. (2004). The Molecular Basis of Diversity in the Photoperiodic Flowering Responses of Arabidopsis and Rice. Plant Physiol. 135: 677–684. DOI: 10.1104/pp.104.042614
FURTHER READING
Hubbard, K., and Dodd, A. (2016). Rhythms of Life: The Plant Circadian Clock. Teaching Tools in Plant Biology: Lecture Notes. Plant Cell, doi/10.1105/tpc.116.tt0416
