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April 11, 2011
Shaping the Leaf Blade – Identification of a New Mechanism to Prevent HD-ZIPIII Dimerization

Leaves are flattened structures perfected for turning sunlight, carbon dioxide and water into sugar and oxygen.  Turning HD-ZIPIII proteins "ON" in some cells and "OFF" in neighboring cells gives the leaf blade its characteristic shape.  The Barton lab is investigating how HD-ZIPIII proteins are kept in the OFF state.   They have recently discovered a series of steps that prevents HD-ZIPIII proteins from coming together to form active dimers.  This work is a step toward understanding how diverse leaf shapes have evolved to adapt to a vast array of environmental conditions.

Leaf cells are specialized to optimize photosynthesis.  Cells in the upper portion of the leaf are tightly packed and dense with chloroplasts to capture light energy.  Cells in the lower portion are more irregularly shaped and loosely arranged to allow better exchange of oxygen and carbon dioxide.  The difference between upper and lower parts of the leaf is also important for making new branches; new buds are made from the base of the upper, and not the lower, side of the leaf.