Transcriptional feedback regulation of YUCCA genes in response to auxin levels in Arabidopsis

Abstract

The IPyA pathway, the major auxin biosynthesis pathway, is transcriptionally regulated through a negative feedback mechanism in response to active auxin levels. The phytohormone auxin plays an important role in plant growth and development, and levels of active free auxin are determined by biosynthesis, conjugation, and polar transport. Unlike conjugation and polar transport, little is known regarding the regulatory mechanism of auxin biosynthesis. We discovered that expression of genes encoding indole-3-pyruvic acid (IPyA) pathway enzymes is regulated by elevated or reduced active auxin levels. Expression levels of TAR2, YUC1, YUC2, YUC4, and YUC6 were downregulated in response to synthetic auxins [1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D)] exogenously applied to Arabidopsis thaliana L. seedlings. Concomitantly, reduced levels of endogenous indole-3-acetic acid (IAA) were observed. Alternatively, expression of these YUCCA genes was upregulated by the auxin biosynthetic inhibitor kynurenine in Arabidopsis seedlings, accompanied by reduced IAA levels. These results indicate that expression of YUCCA genes is regulated by active auxin levels. Similar results were also observed in auxin-overproduction and auxin-deficient mutants. Exogenous application of IPyA to Arabidopsis seedlings preincubated with kynurenine increased endogenous IAA levels, while preincubation with 2,4-D reduced endogenous IAA levels compared to seedlings exposed only to IPyA. These results suggest that in vivo conversion of IPyA to IAA was enhanced under reduced auxin levels, while IPyA to IAA conversion was depressed in the presence of excess auxin. Based on these results, we propose that the IPyA pathway is transcriptionally regulated through a negative feedback mechanism in response to active auxin levels.

Melatonin Regulates Root Meristem by Repressing Auxin Synthesis and Polar Auxin Transport in Arabidopsis

“…The decrease in expression of YUC1 , YUC2 , YUC5 , YUC6 , and TAR2 , together with the effects of melatonin on auxin transport may cause the decrease in IAA levels in roots, at least partially. As reported recently, application of 1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) results in a decay in the transcript levels of YUC1 , YUC2 , YUC4 , YUC6 , and TAR2 in Arabidopsis seedlings (Suzuki et al, 2015). We noticed there is a difference in the endogenous IAA level between this study and previous results (Zhao et al, 2001; Lee et al, 2012), which could be resulted from two possible reasons.…”

Auxin signaling through SCFTIR1/AFBs mediates feedback regulation of IAA biosynthesis

“…27,34,37) We have recently reported that endogenous IAA is downregulated in response to the synthetic auxins 1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D). 38) The feedback regulation of endogenous IAA is accompanied by downregulation of YUC gene expression. 38) Therefore, regulation of YUC gene expression is important in regulating the endogenous IAA level.…”

Small‐molecule auxin inhibitors that target YUCCA are powerful tools for studying auxin function

“…Arabidopsis seedlings were sterilized and grown at 21°C under continuous light and on half‐strength Murashige and Skoog (MS) medium (Invitrogen, Carlsbad, CA, USA) supplemented with 0.8% agar and 1% (w/v) sucrose. To measure primary root length, the wild‐type and YUC1‐overexpressor (Suzuki et al ., ) were grown for 7 or 9 days on agar medium containing 3 μ m of inhibitors in vertically oriented plastic plates. To measure free IAA, the wild‐type seedlings were grown for 6 days on vertically oriented agar medium, transferred to a culture tube containing liquid medium, incubated for 1 day with shaking, and treated with or without inhibitors dissolved in 0.1% (v/v) dimethyl sulfoxide (DMSO) for 3 h. To measure IPyA, the wild‐type seedlings were grown for 7 days on agar medium in vertically oriented plates, transferred to a culture tube containing liquid medium, incubated for 1 days with shaking, and treated with or without inhibitors dissolved in 0.1% (v/v) DMSO for 3 h. To assess gene expression of auxin markers, the wild‐type seedlings were grown for 6 days on vertically oriented agar medium, transferred to a culture tube containing half‐strength MS liquid medium with 1% sucrose, incubated for 1 day with shaking, and treated with 10 μ m inhibitors, 1 μ m IPyA and 100 n m IAA for 3 h. To test for recovery from growth defects caused by BBo or PPBo, wild‐type seedlings were grown 7 days on half‐strength MS plates in the presence of 3, 10 or 30 μ m BBo or PPBo in combination with 0, 1, 10 or 100 n m IAA.…”