No abstract

We describe here the isolation of a novel gene, designated AlSAP, from A. littoralis in a first step to exploit the potential of this halophyte grass as a genetic resource to improve salt and drought tolerance in plants and, particularly, in cereals. The Aeluropus genome contains a single AlSAP gene which has an intron at its 5'UTR. Sequence homology analysis showed that the AlSAP protein is characterized by the presence of two conserved zinc-finger domains A20 and AN1. AlSAP is induced not only by various abiotic stresses such as salt, osmotic, heat and cold but, also by abscisic acid (ABA) and salicylic acid (SA). Tobacco plants expressing the AlSAP gene under the control of the duplicated CaMV35S promoter exhibited an enhanced tolerance to abiotic stresses such as salinity (350 mM NaCl), drought (soil Relative Water Content (RWC) = 25%), heat (55 degrees C for 2.5 h) and freezing (-20 degrees C for 3 h). Moreover, under high salt and drought conditions, the transgenic plants were able to complete their life cycle and to produce viable seeds while the wild-type plants died at the vegetative stage. Measurements of the leaf RWC and of the root and leaf endogenous Na(+) and K(+) levels in AlSAP transgenic lines compared to wild-type tobacco, showed an evident lower water loss rate and a higher Na(+) accumulation in senescent-basal leaves, respectively. Finally, we found that the steady state levels of transcripts of eight stress-related genes were higher in AlSAP transgenic lines than in wild-type tobacco. Taken together, these results show that AlSAP is a potentially useful candidate gene for engineering drought and salt tolerance in cultivated plants.

No abstract

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.