A role for nitrilase 3 in the regulation of root morphology in sulphur‐starving Arabidopsis thaliana

Abstract

SummaryArabidopsis 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 b-cyano-L-alanine hydratase/nitrilase. NIT3 promoter activity is marginal in leaves or roots of vegetative plants and undetectable in bolting and¯owering plants, but its level increases strongly when plants experience sulphur deprivation. No other nitrilase genes respond to sulphur supply/de®ciency. 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 b-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 de®ciency 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 de®ciency, 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.

Occurrence and formation of indole-3-acetamide in Arabidopsis thaliana

“…As it is known that (i) the genes for the IAN-converting isoforms 2 and 3 of A. thaliana nitrilase are active specifically during embryo development (NIT2, Vorwerk et al 2001) and early germination (NIT3, Kutz et al 2002) and (ii) amides may be side-products of nitrilase activity (Bartel and Fink 1994;Piotrowski et al 2001), we examined the conversión of IAN by purified, recombinant NIT1, NIT2 and NIT3 (Fig. 5).…”

“…Those stages of development characterized by high levéis of IAM are also characterized by a high state of activity of the genes encoding nitrilases 2 and 3 (Vorwerk et al 2001;Kutz et al 2002). ii.…”

“…Recently, this was shown to be the case under particular circumstances. In sulphur-starved A. thaliana plants, the NIT3 gene is strongly induced and concomitantly, the turnover of glucobrassicin is intensified over that of the other glucosinolates (Kutz et al 2002). On the other hand, there is strong evidence that, in planta, nitrilases are much more effective compared to the recombinant enzymes in vitro.…”

Impacts of root sulfate deprivation on growth and elements concentration of globe amaranth (Gomphrena globosa L.) under hydroponic condition

“…The aboveground dry matter under sulfate deprivation treatment was decreased significantly by 62.1%, while SO 4 2-deprivation did not reduce root weight (Figure 2). Globe amaranth shoot growth was affected more than root growth upon SO 4 2-deprivation; more prolonged sulfate deprivation generally results in changes of shoot/root biomass ratio in favor of root production , Yang et al 2003, Buchner et al 2004) and root morphology by increasing the total absorptive surface of the root system (Kutz et al 2002, López-Bucio et al 2003. However, the sulfate-deprived plants seemed to have a rapid growth when they were in bloom; their aboveand underground dry weights were much higher than those of sulfate-supplied plants at the end of flowering sampling on October 31.…”

Metabolite profiling of Arabidopsis seedlings in response to exogenous sinalbin and sulfur deficiency

“…2C). Enhanced root growth is a developmental response of plants to nutrient deficiency (Forde and Lorenzo, 2001;Kutz et al, 2002).…”