Auxin: Regulation and its modulation pathways.

Indole-3-acetic acid (IAA), or auxin, is a key regulator of almost all processes of plant growth and development. In general, the auxin biosynthesis, metabolism, and transport systems form a global auxin machinery, which is controlled by a great number of specific genes. The regulation of this auxin system is implemented at least in four functional levels, i.e. biosynthesis, metabolism, transport of auxin, and response to auxin signaling. Not all the genes involved in the operation and regulation of auxin machinery are known to this day, and there are still many uncertainties in our ideas about the functioning of this key plant growth system. The list of genes associated with auxin action expands rapidly. However, only a few of them are likely to be used as viable targets for directed crop improvement in genetic transformation programs. This review reflects our current understanding of the internal regulation mechanisms of the plant auxin system and reveals the most attractive gene targets for use in genetic engineering. [ABSTRACT FROM AUTHOR]