Date: 2019-11-15
Facing the potential food shortage caused by frequent and stressful conditions due to climate changes (drought, flooding, high temperature, etc.), it has been a common goal for many countries around the world to breed for crops with efficient growth and development, and ability to maintain high productivity under adverse environment. Recent discoveries by the research team of Distinguished Research Fellow and Academician Su-May Yu revealed that the above goal can be achieved through maintenance of sugar homeostatic states in plants. The basic knowledge and potential applications generated in this work have been well recognized and the paper was recently published in the highly reputable journal, the Proceedings of National Academy of Science, USA.
Plants are autotrophic organisms capable of supporting their growth and development by carrying out photosynthesis utilizing CO2 in the air and water and minerals in the soil. They can also store fixed carbon in starch and lipids that support other organisms on earth. Mammals, such as humans, rely on glucagon and insulin to control blood sugar levels so that sugar homeostasis is maintained to prevent physiological disturbance. Plants are also in need of keeping sugar homeostatic states. However, because the demand in growth and response to significant environmental changes, plant sugar levels tend to fluctuate in a broader range than in mammals.
Sugar levels in plants are maintained by the balance between their synthesis and utilization. High sugar levels lead to the synthesis of other cellular materials, transport, storage of reserves and cell growth, but also suppression of photosynthesis, degradation of storage nutrients, and response to stresses. On the other hand, low sugar levels induce opposite responses. The molecular mechanisms underlying how the regulation of gene expression by fluctuating sugar levels are able to elicit two sets of opposing responses remain unclear.
Years ago, Dr. Yu’s group was first to discover that the expression of the key enzyme for starch hydrolysis, α-amylase (αAmy), subjected to inhibition by high levels of sugars, and they followed up by carrying out in-depth research on this process. In addition, literature have also shown that the expression of αAmy is induced by stresses and pathogen infections. However, the molecular mechanisms of these regulations are not well understood.
In the current publication, Dr. Yu’s group reported that the expression of αAmy is regulated by the competition between two transcription factors, MYBS1 and MYBS2. When cells are depleted of sugar, MYBS1 enters the cell nucleus to promote αAmy synthesis, whereas when sugar levels are elevated, MYBS2 enters nucleus to inhibit αAmy expression. When cells are in need of sugars, MYBS2 is phosphorylated at the 53th amino acid, leading to its export from nucleus and then be trapped by a group of 14-3-3 proteins in the cytosol, incapable of re-entering the nucleus where it could compete against MYBS1 for the binding to the promoter of αAmy gene. Consequently, MYBS1 in the nucleus is able to enhance the expression of αAmy.
Furthermore, the MYBS2 expression is suppressed by drought, high temperature and osmotic stress, leading to the high level of αAmy expression needed for growth, stress tolerance and high grain yield. This work reveals new insights into why many plants enhance the expression of αAmy under stress, which is probably necessary for maintaining high productivity under adverse environment.
The most seminal discovery reported in this paper for the first time is the on/off molecular switch regulated by sugar provision and depletion for maintaining sugar homeostatic states, which is closely related to plant growth, development and response to the environment. In the future, gene editing techniques could be applied to manipulate the function and expression of MYBS2 and αAmy for the improvements of rice and other cereals in addressing the challenges caused by great crop loss due to climate changes and increased food demand due to rapidly growing population. A US patent has been filed for this technology.
The corresponding author of this seminal paper is Distinguished Research Fellow Su-May Yu who has been collaborating with Professor Chung-An Lu, Department of Life Science, National Central University. The first author is Ms. Yi-Shih Chen, a Ph.D. candidate, who carried out most of the experimental work. Other collaborators include Distinguished Visiting Chair Tuan-hua David Ho, Institute of Plant and Microbial Biology, and Dr. Shu-Yu Lin, Institute of Biochemistry, Academia Sinica. Financial support of this work was generously provided by Ministry of Science and Technology, Academia Sinica, and the Advanced Plant Biotechnology Center at National Chung Hsing University.
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Ms. Pei-Chun Kuo, Media Team, Secretariat, Central Administrative Office, Academia Sinica
(02) 2789-8821,deartree@gate.sinica.edu.tw
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Chang-Hung Chen, Public Affairs Section, Secretariat, Academia Sinica
(02) 2789-8059,changhung@as.edu.tw