Structural analysis of the nit2it1it3 gene cluster encoding nitrilases, enzymes catalyzing the terminal activation step in indole-acetic acid biosynthesis in Arabidopsis thaliana

摘要

A 13.8 kb DNA sequence containing the promoters and the structural genes of the Arabidopsis thaliana nit2it1it3 gene cluster has been isolated and characterized. The coding regions of nit2, nit1 and nit3 spanned 1.9, 1.8 and 2.1 kb, respectively. The architecture of the three genes is highly conserved. Each isoform consists of five exons separated by four introns. The introns are very similar with respect to size and position, but differ considerably in sequence composition. In contrast to thecoding sequences the three promoters are very different in sequence, size and in their repertoire of cis elements, suggesting differential regulation of the three nitrilase isoenzymes by the developmental programme of the plant and by diverse environmental factors. The nit1 promoter was subjected to analysis in planta. Translational fusions placing the nit1 full-length promoter and a series of 5'-deletion fragments in front of the uidA gene encoding beta-glucuronidase (GUS) were used for Agrobacterium tumefaciens-mediated transformation of Nicotiana tabacum. GUS expression was highest in fully expanded leaves and in the shoot apex as well as in the apices of developing lateral buds, whereas the GUS activity displayed by developing younger leaflets wasrestricted to the tips of the expanding leaves. Within the root tissue GUS expression was restricted to the root tips and the tips of newly forming lateral roots. Structural features of the nitrilase gene family and nitrilase gene expression patterns arediscussed in context with current knowledge of auxin biosynthesis and auxin effects on different tissues. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession number Y07648.