Present address: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102, USA.
A role for nitrilase 3 in the regulation of root morphology in sulphur-starving Arabidopsis thaliana
Article first published online: 26 APR 2002
The Plant Journal
Volume 30, Issue 1, pages 95–106, April 2002
How to Cite
Kutz, A., Müller, A., Hennig, P., Kaiser, W. M., Piotrowski, M. and Weiler, E. W. (2002), A role for nitrilase 3 in the regulation of root morphology in sulphur-starving Arabidopsis thaliana. The Plant Journal, 30: 95–106. doi: 10.1046/j.1365-313X.2002.01271.x
- Issue published online: 26 APR 2002
- Article first published online: 26 APR 2002
- Received 25 June 2001; revised 2 January 2002; accepted 10 January 2002)
- indole-3-acetic acid;
- root system development
Arabidopsis thaliana expresses four nitrilases, three of which (NIT1, NIT2 and NIT3) are able to convert indole-3-acetonitrile to indole-3-acetic acid (IAA), the plant growth hormone, while the isozyme NIT4 is a β-cyano-l-alanine hydratase/nitrilase. NIT3 promoter activity is marginal in leaves or roots of vegetative plants and undetectable in bolting and flowering plants, but its level increases strongly when plants experience sulphur deprivation. No other nitrilase genes respond to sulphur supply/deficiency. Neither N- nor P-deprivation cause detectable changes in NIT3 promoter activity. In transgenic plants expressing uidA under the control of the NIT3 promoter (NIT3p::uidA), sulphate deprivation leads to the appearance of β-glucuronidase activity in shoots and particularly in roots, most strongly in the conductive tissues and lateral root primordia. Deletion analysis allowed localization of the sulphur-responsive element to a 317 bp segment of the NIT3 promoter encompassing nt −2151 to −1834 upstream of the transcriptional start point. Both nitrilase polypeptide and nitrilase activity were also induced by sulphur starvation. NIT3 promoter activity was strongly induced by O-acetylserine, suggesting that, as is the case with enzymes of sulphate assimilation, sulphate deficiency may be communicated to NIT3 via an increase in the level of the cysteine precursor, O-acetylserine. During sulphur deprivation, a preferential depletion of the pool of the indole-3-acetonitrile precursor glucobrassicin compared with that of total glucosinolates was noticed. In the absence of an external sulphate supply, plants developed longer roots with a higher number of lateral roots. The increased growth of the root system occurred at the expense of shoot growth which was retarded under conditions of sulphur starvation. Taken together, these results suggest that a regulatory loop appears to exist by which sulphate deficiency, through an increase in glucobrassicin turnover and nitrilase 3 accumulation, initiates the production of extra auxin leading to increased root growth and branching, thus allowing the root system to penetrate new areas of soil effectively to gain access to fresh supplies of sulphur.