The activity of proteins responsible for the processes that plants use to deal with drought conditions has been revealed
It turns out that humanity is not the only one who must make rapid changes to deal with the climate crisis. Even plants, which until now grew in a water-rich environment, have to deal with extreme situations, which are characterized by a severe lack of water and moisture. How do they do it? Researchers at Tel Aviv University have uncovered a central mechanism in plants that helps them deal with dry conditions. These are proteins that drive and regulate a small signal molecule, which controls two essential processes: the closing of the leaf pinnae to prevent water loss and the growth of a branched set of lateral roots that absorb water from the soil. According to the researchers, understanding the response mechanisms of plants to the changing environment may make a significant contribution to agriculture in an era of climate change, thus improving food security in the world.
Close the pawns
The international research, which lasted 6 years and included many stages, was led by Dr. Yutsin Zhang and Prof. Elon Shani from the School of Plant Sciences and Food Security at the George S. Wise Faculty of Life Sciences, and researchers from the Weizmann Institute, Switzerland, Germany, the USA and Denmark participated in it.
"Understanding the response of plants to their changing environment is very important in an era of rapid climate change, and has great significance for agricultural crops that feed humanity," says Prof. Shani. "It has been known for a long time that one of the plant's responses to a lack of water is the closing of the leaves - small openings in the leaves that allow contact with the environment. When the leaves are open, the entry and exit of gases increases, the photosynthesis process is accelerated, and the plant produces energy, grows and produces fruit. But when the plant wishes to preserve the little water available to it, it closes the leaves and reduces the process of water evaporation through the leaves. This is an extremely sensitive and fast mechanism, by means of which the plant maintains the correct balance at every moment: it opens or closes leaves within seconds to minutes in response to any small change in water availability, temperature, and the amount of light."
According to the researchers, already in the 60's of the last century it became clear that one of the main substances in the control mechanism of piony is a plant hormone called ABA - A small signal molecule that signals to the pions that they must close. in the presence of a high level of ABA The pawns close, and vice versa: in his absence they open.
The prevailing belief for years was that theABA Formed in the roots in response to dryness in the soil, then climbs up the stem to the leaves to close the petioles. In the current study, the researchers examined this hypothesis, and found that the reality is much more complex. The article was published in the journal Science Advances.
A 'storehouse' of leaf signaling molecules
"For the purpose of the research, we used the model plant Arabidopsis (white cotton plant), and we used a wide range of advanced techniques from the field of molecular genetics: creating mutations in genetic editing, activation and silencing of genes involved in the process in specific cells, physiological characterizations with advanced equipment and even transport tests of ABA in the eggs of frogs. We also used a combination of sophisticated microscopes with different chemical and genetic methods for fluorescent marking to locate the exact location of a molecule in the plant ABA and the proteins involved", explains Prof. Shani.
The findings surprised the researchers. They discovered that the signal molecule ABA It is stored in a 'dormant' state in the leaves themselves, in cells called mesophyll cells, which play a central role in the photosynthesis process. This storage is actively carried out by two carrier proteins (transporters), which were not known until now, ABCG17 and-ABCG18, responsible for transferring theABA Outside the cell, through the cell membrane, into the mesophyll cells. here passes theABA into an inactive state by binding to a sugar molecule, and is stored over time.
Quick response to changing conditions
To test the role of the two new proteins, the researchers created different mutations in the genes that produce them, and performed a variety of additional experiments that affected the activity of the proteins in time and space. They found that changes in the production of the proteins and their activity cause fluctuations in the transfer and storage of the moleculesABA in the plant, and that in the absence of the proteins theABA Free, arrives in high concentrations in the pores and encourages their closure. According to the researchers, this mechanism allows plants to respond quickly to changing environmental conditions. Specifically, when the plant feels drought stress, the amount and activity of both proteins decrease, theABA 'Wakes up from his slumber', and the peonies close in a short time.
The researchers also found that the long-term movement of the hormoneABA In the plant it is the opposite of what has been thought until now: through the transport bundle system, which is the equivalent of our blood system, theABA A large distance - precisely from the leaves to the roots, and not the other way around. This movement is also controlled by the same carrier proteins, ABCG17 and-ABCG18: A decrease in the activity of the two proteins in the leaf causes a decrease in storage ABA in the mesophyll cells in a 'dormant' state, and theABA The free moves in the direction of the root. accumulation ABA The root controls the development of lateral roots, which absorb more water from the soil.
"In this study, we added an important layer to understanding the mechanism by which the plant copes with changing conditions such as lack of water. For the first time, we discovered a control mechanism by which the plant stores signal molecules in a 'storehouse', and releases them under the desired conditions. This discovery may make a significant contribution to agriculture in an era of rapid climate change, thereby improving food security in the world. In follow-up studies, we are now examining similar mechanisms in two important agricultural crops: tomato and rice", Prof. Shani concludes.
