The Shape of Plants: Microtubule Dynamics and Plant Adaptation

点击翻译按钮获取中文摘要

This research program aims to identify the mechanisms by which plants integrate signals from their immediate surroundings to control the growth transitions that optimize their development. These mechanisms underline the evolutionary processes that have enabled plants to colonize and thrive in harsh environments. The research objectives will therefore lead to new strategies for enhancing plant performance and productivity under challenging climatic conditions. Our work focuses on understanding the properties and function of dynamic protein polymers known as microtubules. These 25 nm diameter tubular elements were first identified 50 years ago in plant cells but are now recognized as essential components of all eukaryotic cells in which they form the machinery that drives cell division, growth and motility. To form these machines, microtubules must undergo rapid growth and shrinkage through addition or removal of protein subunits known as tubulins. These processes are controlled by microtubule-associated proteins. Our pioneering work on two such proteins, CLASP and MOR1, form the foundation for the proposed research. One objective of this research program is to understand how plants control the transition from cell division to cell elongation. We recently discovered that the CLASP protein is required for normal distribution and activity of the plant growth hormone auxin. We demonstrated that CLASP tethers compartments carrying auxin transporters to microtubules, thus preventing their degradation. Loss of CLASP causes cells to undergo fewer rounds of division and to enter the elongation phase prematurely, resulting in fewer cells and dwarf plants. Determining how CLASP activity is governed is therefore critical for understanding how cells transition from proliferation to terminal growth. We have recently found that the plant steroid hormone brassinolide controls CLASP expression but that its signaling activities are, paradoxically, controlled by CLASP. Our proposed strategies to dissect this fascinating regulatory feedback mechanism will have far reaching implications for understanding how hormone-based signaling networks optimize plant growth. Abiotic stresses and pathogens dramatically alter plant growth. Microtubules are often disrupted as part of the adaptation to stresses such as cold, salt or exposure to heavy metals. Using a chemical-genetics approach, we identified a mutation in the microtubule-associated protein MOR1 that alters the normal response to hyperosmotic stress. We will use this mutant to identify and manipulate the signaling pathways that enable plants to adapt to salt stress or drought. In addition, through a gene expression profiling initiative, we identified 13 genes that show altered expression when treated with a drug that simulates stress-induced microtubule disruption. Some of these genes are known to be involved in pathogen or abiotic stress responses and will therefore form the foundation of a long-term strategy to improve resistance of crop plants to pathogens and abiotic stress. Our third goal will refine the understanding of how microtubules control the enzyme complexes that produce the world’s most abundant biopolymer cellulose. The ability of cellulose to resist tension makes it a key determinant of both the rate and direction of cell expansion, which is critical for plant performance but also of relevance for many industrial applications. We will use state-of-the-art imaging technology to determine how changes in microtubule activity alter the properties of cellulose. These complementary initiatives aimed at understanding plant growth and adaptation will address critical issues facing agriculture and forestry, and provide opportunities for the biofuels industry.