Plant memory in changing and fluctuating climates

Recent climate change has shifted the flowering time of many plant species. During the International Year of Biodiversity in 2010, this flowering time shift has been highlighted because coordination between pollinating animals and plants could be at risk. Professor Dr. Kentaro Shimizu, a plant biologist at the University of Zurich, and Japanese colleagues have shown that a gene for plant flowering works as a memory of temperature during the past six weeks, and would be useful for accurate projection (prediction) of the plant response to temperature changes.

Many plants flower in spring by detecting prolonged cold temperature (called vernalization). In natural conditions, temperature shows day/night, day-by-day, and weekly fluctuations that are often inconsistent with seasonal trends. Without memory of past temperatures, it would be difficult for plants to detect seasons in natural, noisy environments. A major obstacle to projecting (predicting) flowering response has been the lack of visible change during the cold duration. An evolutionary biologist at the University of Zurich, Kentaro Shimizu, and a PhD student, Masaki Kobayashi, in collaboration with Japanese researchers led by Dr. Hiroshi Kudoh, measured the internal state of plants by quantifying the expression level of a key flowering-time gene called FLC. Such molecular measurements, undertaken over two years, showed that the regulatory network of the FLC gene stores the information of temperatures over the past six weeks.

Time series analysis revealed that as much as 83% of the variation in FLC expression is explained solely by the temperature for the previous six weeks, but not by the temperatures over shorter or longer periods. The projection (prediction) from the model based on this time series analysis fits the gene expression pattern under contrasting temperature regimes in artificial transplant experiments. This indicates that such modeling incorporating the molecular basis of flowering-time regulation will contribute to projecting plant responses to future climate changes.

The researchers studied a perennial plant species, Arabidopsis halleri, which is distributed from lowland to alpine regions in Europe and East Asia, and is a close relative of a model plant, Arabidopsis thaliana. The molecular basis of flowering response has been extensively studied in the laboratory using Arabidopsis thaliana, and it was known that FLC is the key regulator in temperature-dependent flowering. However, little was known about the regulation in natural fluctuating environments. First, the researchers isolated the FLC gene from Arabidopsis halleri and confirmed that it regulated flowering in an overexpression experiment. Then the tissues of six individuals of this perennial species were collected every week for two years in the natural environment, even during storms or if it rained or snowed. In their article published in the journal Proceedings of the National Academy of Sciences, USA, the researchers showed that the memory and buffering functions of FLC, which last for about six weeks, act as a filter to extract the seasonal cue from the noisy, natural environment.

2010 is the International Year of Biodiversity. While the distribution changes of organisms in response to global warming has often been discussed, phenotypic and evolutionary organismal responses due to climate change have not yet been investigated sufficiently. The research highlights that molecular biology and systems biology could provide powerful tools to study the effect of climate change when combined with ecology.

Literature:

Shinichiro Aikawa, Masaki J. Kobayashi, Akiko Satake, Kentaro K. Shimizu, and Hiroshi Kudoh: Robust control of the seasonal expression of the Arabidopsis FLC gene in a fluctuating environment. Proceedings of the National Academy of Sciences, USA, doi/10.1073/pnas.0914293107.