Promoter of the AlSAP gene from the halophyte grass Aeluropus littoralis directs developmental-regulated, stress-inducible, and organ-specific gene expression in transgenic tobacco.

In our recent published work it has been demonstrated that AlSAP, a gene encoding an A20/AN1 zinc-finger protein (stress-associated protein) of the C4 halophyte grass Aeluropus littoralis, is inducible by various abiotic stresses and by hormonal stimuli. To further investigate the regulation of the gene, a 586-bp genomic fragment upstream of the AlSAP translated sequence has been isolated, cloned, and designated as the "Pr ( AlSAP )" promoter. Sequence analysis of "Pr ( AlSAP )" revealed the presence of cis-regulatory elements which could be required for abiotic stress, abscisic acid (ABA), and salicylic acid (SA) responsiveness and for tissue-specific and vascular expression. The Pr ( AlSAP ) promoter was fused to the β-glucuronidase (gusA) gene and the resulting construct transferred into tobacco. Histochemical assays of stably transformed tobacco plants showed that Pr ( AlSAP ) is active in this heterologous C3 system. While full-length gusA transcripts accumulated in whole 15, 30, and 45-day-old plants, GUS histochemical staining was only observed in leaves and stems of 45-day-old, or older, transgenic seedlings. Histological sections prepared at this stage revealed activity localized in leaf veins (phloem and bundle sheath) and stems (phloem and cortex) but not in roots. Furthermore, gusA transcripts accumulated in an age-dependent manner with a basipetal pattern in leaf and stem tissues throughout the plant. In flowers, GUS expression was detected in sepals only. The accumulation of gusA transcripts was up-regulated by salt, dehydration, ABA, and SA treatment. Altogether, these results show that, when used in a heterologous dicot system, Pr ( AlSAP ) is an age-dependent, abiotic-stress-inducible, organ-specific and tissue-specific promoter.