Poster: Hormones

Abs # 651: Physiological and genetic dissection of the mechanism of action of antiauxin p-chlorophenoxyisobutyric acid in Arabidopsis root growth

Presenter:	Rahman, Abidur , abidur@popx.tokai.jaeri.go.jp
Authors	Rahman, Abidur  (A)   Ooura, Chiharu  (B)   Uchimiya, Hirofumi  (C)   Tanaka, Atsushi  (A)   Oono, Yutaka  (A)
Affiliations:	(A): Plant Resources Research Group, Japan Atomic Energy Research Institute (B): Advanced Science Research Center, Japan Atomic Energy Research Institute (C): Institute of Molecular and Cellular Biosciences, The University of Tokyo

p-chlorophenoxyisobutyric acid (PCIB) has been used as an antiauxin for more than five decades and believed to compete with auxin at it’s receptor site. Previously we found that PCIB inhibited the auxin-induced gene expression in Arabidopsis. However, the mechanism of antiauxin action of PCIB is still unclear. In the present study we have used both physiological and molecular approaches to characterize this compound. Our physiological data revealed that PCIB has a bi-phasic response on the growth and development of Arabidopsis roots. At a high concentration range (10-20 mM) PCIB completely inhibited the lateral root development and to some extent the root growth while at a low concentration range (1-10 nM) it promoted the root growth and lateral roots. The partial resistance of the auxin resistant mutants at higher concentration of PCIB and the inhibition of Aux/IAA expression at that concentration suggest that PCIB works on the auxin signaling pathway. The bi-phasic action of PCIB was further confirmed by investigating the effect of PCIB on ubiquitin proteasome dependent degradation of IAA/AUX protein. Prolonged incubation of the Arabidopsis roots in high concentration of PCIB induced ectopic auxin maximum and multiple meristems in the distal root tip of the primary root. The screening of antiauxin (PCIB) resistant (aar) mutants led us to discover mutants with novel characters. One of the mutant line aar1 shows longer hypocotyls, produces more lateral roots compared with wild-type and exhibits altered responses to 2,4-D and IBA for root growth, suggesting that mode of action of PCIB is integrated with auxin signaling pathway.