-chlorophenoxyisobutyric acid impairs auxin response in arabidopsis root

Ono, Yutaka; Oura, Chiharu*; Rahman, A.; Aspuria, E. T.; Hayashi, Kenichiro*; Tanaka, Atsushi; Uchimiya, Hirofumi*

PCIB (-chlorophenoxyisobutyric acid) is known as a putative antiauxin and is widely used to inhibit auxin action, although the mechanism of PCIB-mediated inhibition of auxin action is not characterized very well at molecular level. In the present work, we showed that PCIB inhibited BA::GUS expression induced by IAA, 2,4-D and NAA. PCIB also inhibited auxin dependent DR5::GUS expression. RNA hybridization and quantitative RT-PCR analyses suggested that PCIB reduced auxin-induced accumulation of transcripts of genes. In addition, PCIB relieved the reduction of GUS activity in transgenic line in which auxin inhibits GUS activity by promoting degradation of the AXR3NT-GUS fusion protein. Physiological analysis revealed that PCIB inhibited lateral root production, gravitropic response of roots and growth of primary roots. These results suggest that PCIB impairs auxin signaling pathway by regulating Aux/IAA protein stability, and thereby affects the auxin-regulated Arabidopsis root physiology.