While it has long been appreciated that mechanical stimuli like gravity, touch, and osmotic pressure are important regulators of plant growth and development, the molecular mechanisms by which plant cells perceive mechanical force is not yet understood. In animal and bacterial systems, mechanosensitive (MS) ion channels mediate the perception of many mechanical stimuli. In plants, a family of proteins related to the bacterial MS channel MscS are implicated in mechanosensory signal transduction. In the model flowering plant Arabidopsis thaliana, two members of this MscS-Like (MSL) family are targeted to the poles of chloroplasts where they control plastid shape and size. How plastids (or organelles in general) take their shape is an area of recent excitement, and the role that mechanosensory systems might play in such a process has not yet been addressed. The objectives of this project are to: 1) further delineate how and why MSL2 and MSL3 are localized to the poles of plastids; 2) address the evolutionary history of MscS-Like proteins by determining their function in Synechocystis sp. PC6803, cyanobacteria that share a common ancestor with plant chloroplasts, and 3) develop nongreen plastids in Arabidopsis thaliana as a model system for studying organelle morphology control. These studies address two general goals: (i) to further our understanding of plant cell biology and how plants use MS ion channels to sense and respond to important stimuli; and (ii) to advance our knowledge of the basic principles of mechanotransduction and organelle shape determination.
Broader impacts. The PI has been involved in women's advocacy for many years, and is strongly committed to expanding opportunities for women and minorities in STEM fields. The Undergraduate Plastid Project will be developed as a platform for undergraduate research, and will be integrated into an existing Pathway for undergraduate studies in imaging technologies at Washington University. A high school teacher-intern will participate in this research program during two consecutive summers, develop innovative curricula, and ultimately benefit the students at his or her school. Finally, a Washington University doctoral student will be provided an important training environment.
We often think of plants as static, unmoving and unfeeling. In fact, plants are constantly sensing and responding to incoming information about their environment, though their responses may not be easily observed. One type of information to which plants must respond is mechanical force—such as gravity, touch, or tension. We are interested in a class of proteins, called mechanosensitive channels, which serve to sense and respond to mechanical force. Though these mechanosensitive channels were first characterized in bacteria, they are also found in plants and some fungi. The research supported by this award was designed to study how two mechanosensitive channels function in the model organism Arabidopsis thaliana, a small flowering plant. The results of our experiments gave us a number of new insights into how mechanical forces are sensed and perceived by plants, by their cells, and by the organelles inside their cells. In particular, we learned how the molecular machines that control the division and propagation of chloroplasts (the organelles inside plant cells that conduct photosynthesis) are affected by mechanical force, and how organelles deal with mechanical force from inside the cell. We also learned about the evolutionary relationship between the strategies used by bacteria and by plants to respond to similar environmental challenges.
