How cell regulate their expansion is central question in modern biology. In plants, asymmetric cell expansion is a primary determinant of the size and shape of organs. However, very little is known regarding the molecular mechanisms underlying the regulation of cell expansion in plants. A pair of receptor-like kinases from Arabidopsis, called AIK1 and AIK2, has been identified that directly interact with ACC synthase, the enzyme that catalyzes the rate-limiting step in the biosynthesis of the plant hormone ethylene. Genetic studies have revealed that these AIK genes play an important role in regulating cell expansion in root cells. Ethylene promotes radial expansion of plant cells, and the radial swelling phenotype in the aik1/aik2 double mutant was found to be dependent on ethylene. This, coupled with the observation that these proteins directly interact with ACC synthase, suggests that these AIK genes are involved in the interaction between ethylene and directed cell expansion. This interaction will be further explored by precisely delineating the effects of the AIK mutations on the growth characteristics of the root and by determining if these genes directly regulate features of the cell involved in directing cell elongation, such as the cell wall. The role of ethylene in the aik mutant phenotype will be explored using genetic and biochemical approaches. Finally, additional targets of these AIK kinases will be sought using a simple interaction screen in yeast. This research will shed light on how plants regulate cell elongation, which is crucial to understanding the development of plant form.The proposal will also provide interdisciplinary training opportunities for undergraduate and graduate students in diverse areas including cell biology, plant physiology, molecular genetics, and biochemistry.
