Characterisation of MAX1 and its role in axillary shoot branching in Arabidopsis thaliana

Lateral shoot branches are usually derived from lateral buds laid down in the axils of leaves. Lateral buds can remain dormant or they can activate to produce a branch. This decision is influenced by a wide range of factors, including the position of the axil along the primary shoot axis, the developmental stage of the plant, the availability of nutrients and light and the proximity of neighboring plants. Thus, the regulation of shoot branching provides an ideal system in which to study the integration of environmental and developmental signals in the control of plant development. Moreover, canopy structure is an important trait in agriculture, horticulture and forestry and hence a better understanding of the way in which shoot branching is regulated will have wide application. It is known for a long time that the phytohormone auxin plays a central role in the regulation of shoot branching The concept of apical dominance proposes that apically derived auxin is transported down the plant where it inhibits the outgrowth of axillary buds. However, the mechanism by which auxin regulates bud growth is unclear. In the laboratory of Prof. Ottoline Leyser (University of York, UK) genes could be identified (MAX1-4) which are mediating the inhibiting effect of auxin on axillary bud growth. There are strong indications that 3 of these genes (MAX1/3/4) are involved in the production of a carotinoid-derived signaling molecule. MAX1 belongs to the family of P450 monooxygenases, enzymes catalysing oxidation reactions on a diverse set of compounds. The aim of the proposed work is the functional characterisation of MAX1 by genetic, biochemical and molecular-biological means, which should lead to new insights in how auxin regulates axillary bud growth and might also result in the identification of a novel hormone acting downstream of auxin in the control of shoot branching .