Gene-Based Tool Predicts Cherry Blossom Blooming Times

Japan is well-known for its sakura, or cherry blossoms, which bloom in the southern Kyushu region and ascend to the far north of Hokkaido in the spring. Somei Yoshino, the most common cultivar of cherry trees, is the quintessential springtime symbol. At each location, the cloned trees flower simultaneously, producing a brief burst of white-pink blossom that mesmerizes both locals and visitors.

Somei Yoshino flowering forecasts are carefully studied months before flowering, as visitors schedule their trips and locals arrange festivals and celebrations. However, due to climate change, the flowering times of these cherry trees are changing and becoming more difficult to predict.

Recently, scientists at the Forestry and Forest Products Research Institute and Kyushu University created a model that utilizes gene activity to forecast when the buds of Somei Yoshino cherry trees will wake up from dormancy.

The study, which was published on September 19^th, 2024, in the journal Plants, People, Planet, can also help to increase the precision of flowering forecasts by drawing attention to the possibility that climate change could endanger flowering in southern Japan.

Cherry tree buds must go through the endodormancy and ecodormancy stages of dormancy before they can bloom. Endodormancy must be broken by a period of sufficiently cold winter temperatures, and ecodormancy must be broken by a springtime heat input.

This need for both cooling and heating means that flowering times can be very unpredictable. Depending on the temperature of autumn, winter, and spring, flowering could be early, delayed, or hindered altogether.”

Atsuko Miyawaki-Kuwakado, Study First Author and Research Fellow, Kyushu University

When eco dormancy ends, the buds open and grow rapidly. It can be challenging to determine when the previous stage of endodomancy has ended because the buds don't seem to change. However, according to Miyawaki-Kuwakado and senior author Professor Akiko Satake of Kyushu University's Faculty of Science, figuring out the timing of this crucial moment could be revealed by examining the inner workings of the bud.

From October onwards, the researchers collected leaf and bud samples from Yoshino cherry trees in three locations across Japan: Fukuoka in the south, Tsukuba in the center, and Hokkaido in the north, to capture a snapshot of which genes were most active at each time.

The researchers discovered that the buds of Yoshino cherry trees went through five major gene activity patterns in early summer, summer, autumn, winter, and spring, with each activity pattern closely correlated with temperature.

The research team then concentrated on the activity, or expression levels, of a subset of genes known as DAM, which is associated with bud dormancy. Out of the six DAM genes studied, the researchers discovered that DAM4 activity was critical in maintaining endodormancy.

We saw that at the start of winter, DAM4 was highly expressed, but as each day passed with temperatures below 10.1 °C, the activity of DAM4 decreased. Once below a certain threshold, the buds awoke from dormancy and flowered when experimentally heated.”

Akiko Satake, Study Senior Author and Professor, Faculty of Science, Kyushu University

Using a model based on DAM4 activity, the researchers concluded that Yoshino cherry trees require approximately 61 days of temperatures below 10.1 °C for endodormancy to break. Using historical temperature data from the Japan Meteorological Agency, the team estimated that the breaking of endodormancy was delayed by 2.3 days per decade between 1990 and 2020.

Forecasters may utilize the projected awakening times going forward to more accurately predict when the Yoshino cherry buds will open for flowering. The researchers also intend to improve the model to forecast how climate change will impact flowering.

Miyawaki-Kuwakado concluded, “Without sufficient cool days over winter, endodormancy cannot break and Yoshino buds cannot flower. Therefore, it is important to predict the impact of global warming, particularly in Japan’s southern region, so that we can try to develop strategies to mitigate it.”