Question

TRANSPORT INHIBITOR RESPONSE (TIR) proteins, AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins, and AUXIN RESPONSE FACTOR (ARF) proteins all play key roles in regulating the expression of AUXIN RESPONSE GENE (ARG) genes that harbour AUXIN RESPONSE ELEMENTS (AREs) in their promoter sequences in response to auxin. Describe the functional role of TIRs, Aux/IAAs and ARFs in regulating the expression of ARG genes that harbour AREs in their promoters in response to auxin expression.

Answer 1

Ans. The Aux/IAAs gene family comprises of 29 members and encodes short lived nuclear proteins. The characteristics of Aux/IAA proteins is the presence of four highly conserved domains (I-IV), which imparts the functional properties of the proteins. Domain I mediates the transcriptional represssion of the proteins, domain II mediates protein degradation, domains III and IV are responsible for the homo and heterodimerization with other Aux/IAA proteins as well as heterodimerization of ARFs

ARFs are encoded by large gene family comprising of 22 members. Transcription factors bound specifically to auxin responsive cis acting elements. These elements are found in promoters of early auxin responsive genes. Aux/IAA negatively regulate the abundance of ARFs and subsequently the expression of auxin responsive genes.