T-DNA trapping of a cryptic promoter identifies an ortholog of highly conserved SNZ growth arrest response genes in Arabidopsis

A T-DNA tagged Arabidopsis locus, A37, identified by a promoter-trap aph(3')II reporter gene fusion expressed in calli and roots, encodes an ortholog of evolutionarily conserved SNZ growth arrest response proteins. Gene A37 is located on chromosome 3-35, lacks introns, and shares considerable sequence identity with HEVER1 from rubber tree, SLEXORFA-1 from Stellaria longipes, SNZ1 from yeast, and SNZ-homologs from bacteria and archaebacteria. Southern DNA hybridization and physical mapping data show that A37 is a single copy gene, but sequence similarity to expressed sequence tags (ESTs) suggests that at least two other SNZ-homologs are present in Arabidopsis. The A37 gene is abundantly expressed in cultured callus tissues and at lower levels in leaves, stems and roots. In the promoter-trap locus a37, the T-DNA-linked aph(3')II reporter gene is transcribed oppositely to the A37 gene by a cryptic promoter located 0.52 kb upstream of the A37 coding region. Promoter deletion studies with uidA-reporter gene constructs show that the cryptic promoter consists of regulatory sequences located in both promoter and transcribed regions of the A37 gene that activate transcription only in roots. The a37 promoter trap is thus controlled by transcriptional regulatory sequences that function as an active promoter only in linkage with a promoterless reporter gene introduced artificially into the Arabidopsis genome by a T-DNA tag. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.