PIS1, a negative regulator of the action of auxin transport inhibitors in Arabidopsis thaliana

Abstract

In order to clarify the mechanism underlying the polar auxin transport system, the pis1 mutant in Arabidopsis thaliana that is hypersensitive to N‐1‐naphthylphthalamic acid (NPA), an auxin transport inhibitor was isolated and characterized. Whereas the pis1 mutant is normally sensitive to phytohormones, auxins, cytokinin and ethylene precursor, this mutant is hypersensitive to NPA over the broad spectrum of its effects such as growth of seedlings, root elongation, root gravitropism, root phototropism and root curling. This result indicates that the pis1 mutant is specifically affected in the polar auxin transport system. This result also defines a genetic factor controlling both gravitropism and phototropism, and strongly indicates the involvement of auxin transport during both tropic responses. NPA, 2,3,5‐triiodobenzoic acid (TIBA) and 9‐hydroxyfluorene‐9‐carboxylic acid (HFCA) represent different classes of auxin transport inhibitors. The pis1 mutation conferred hypersensitivity to both NPA and TIBA but not to HFCA. These results show the genetic separation of the actions of NPA/TIBA and of HFCA. The PIS1 gene product might be specifically involved in the response pathway of NPA/TIBA, leading to interference with auxin‐efflux carriers, and might act as a negative regulator of the action of NPA/TIBA.

Biosynthesis, conjugation, catabolism and homeostasis of indole-3-acetic acid in Arabidopsis thaliana

“…Identification of components of both the influx and efflux carriers has allowed detailed analysis of expression profiles (Galweiler et ai., 1998;Milller et at., 1998a;Swamp et at., 2001). The pisl mutant was shown to be hypersensitive to NPA, and it has been proposed that PISl acts as a negative regulator of the action of the efflux carrier inhibitors NPA and TIBA (Fujita and Syono, 1997). Mutations in AUXl lead to auxin-resistant agravitropic roots and reduced numbers of lateral roots.…”

Morphometric analysis of root shape

“…None of these methods, however, is practical for high‐throughput analysis, and they quantify short‐term effects of physiological stimuli rather than the root developmental pattern. Some assessments of root‐growth patterns are based on measurements of angular deviation of the root tip from the vertical axis (Fujita & Syono, 1996; Rutherford & Masson, 1996; Fujita & Syono, 1997; Marchant et al ., 1999). However, this parameter is not applicable to the description of roots with complex geometry.…”

Root Tropism

“…In addition to gravitropism, pharmacological analysis has demonstrated that auxin-dependent asymmetric growth is required for root phototropism (Fujita and Syono, 1997). However, the molecular machinery required to establish an auxin gradient in response to light perception remains unclear.…”

“…However, the molecular machinery required to establish an auxin gradient in response to light perception remains unclear. As the roots of PIS1 mutants exhibit slightly reduced phototropism and gravitropism (Fujita and Syono, 1997), it is possible that PIS1-mediated auxin transport may contribute to the establishment of a phototropic auxin gradient. As the roots of PIS1 mutants exhibit slightly reduced phototropism and gravitropism (Fujita and Syono, 1997), it is possible that PIS1-mediated auxin transport may contribute to the establishment of a phototropic auxin gradient.…”