Auxin

Auxins are phytohormones responsible for nastic movements and tropisms. They also participate in a wide variety of phenomena within the plant cell [1]. The auxin molecule is relatively simple butperforms a dozen functions in plants [2]. Plants, although lacking the nervous system possessed by animals, have a hormonal long distance communication by which cells translate the hormonal signal into aspecific response. Transportation of auxin in plants is polar, i.e. a stem segment should always have basipetal movement; in contrast, a root segment will have acropetal movement.
Estelle andLeyser simultaneously published their discoveries of transport inhibitor response 1 (TIR1) protein, which is a soluble protein integrate to the F-box protein. TIR1 is responsible for ubiquitination ofproteins that will be degraded by the proteasome, and it also operates as an auxin receptor [3, 4]. TIR1 protein and auxin influence growth, development, and cell multiplication in plants. In addition,the protein TIR1 acts to increase the expression of certain genes associated with growth [2].
The hormone travels to the roots and migrates into the nucleus of root cells in the plant where it iscollected by a protein called TIR1. TIR1 protein is part of a protein complex called ubiquitin protein ligase SCF(TIR1). SCF(TIR1) and auxin join another protein that restrains the expression of aparticular group of genes [1]. This triple binding activates cell growth and development and then auxin disappears as part of the cycle.
TIR1 is a unique receptor hormone in all living organisms and is thefirst case of ubiquitin ligase-complex being regulated by auxin. The manner in which the auxin controls gene expression is still uncertain. Both studies also explain the complexity of auxin throughthe identification of auxin-mutant in Arabidopsis [3, 4]. TIR1 protein was recognized and established as part of the F-box protein. This retains a component of protein called ubiquitin ligase-complex...