689 / 2019-05-01 10:54:39

The gain-of-function mutation of IAAX results in defective auxin-related phenotypes in Arabidopsis

gain-of-function,Arabidopsis,Auxin,Aux/IAA

Plant Hormones > Plant Hormones

Aux/IAA proteins are early auxin responsive short-lived transcriptional repressors, which negatively regulate auxin signaling by interplay with ARFs in plants. In this study, one of these Aux/IAA, IAAX is shown to play role in Arabidopsis development using transgenic plants expressing the gain-of-function form of IAAX (IAAXP75S) under the control of dexamethasone (DEX) inducible promoter, in which IAAX protein was mutated by changing Pro-75 to Ser-75 in conserved domain II. These transgenic plants had higher accumulated transcripts and proteins of IAAX by DEX. The IAAXP75S OX plants show defective auxin-related phenotypes, such as short primary root, less lateral root formation, upcurled leaves, impaired tropic responses, insensitive to exogenous auxin, hypocotyl elongation by high temperature. We found that IAAX transcripts specifically express during lateral root formation and the mutation of IAAX leads to increase protein stability by inhibition of ubiquitin-ligase pathway, resulting in transcriptional repression of auxin-responsive genes. Especially, the transcripts of LBD16 and LBD29 significantly decreased dependently on stabilized IAAX, and IAAX physically interacts with ARF7 and ARF19, which directly activate the transcription of LBD16 and LBD29. These results strongly suggest that the stabilized IAAX might be repress the expression of LBD16 and LBD29 through inhibition of ARF7 and ARF19 activity for inhibition of lateral root development.