A glucocorticoid-inducible transcription system causes severe growth defects in Arabidopsis and induces defense-related genes (original) (raw)
Related papers
Transgenic Research
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.
Regulation of Gene Expression in Plants
In almost all of the areas of gene expression control except one, plant research has lagged considerably behind studies in yeast, insects and vertebrates. Advances in animal gene expression control have also benefited plant research, as we continue to find that much of the machinery and mechanisms controlling gene expression have been preserved in all eukaryotes. However, there are some interesting differences in gene structure and regulation between plants and animals. First, vertebrate genes can be quite large, often spanning tens of thousands of base pairs and usually separated by numerous large introns, whereas plant genes tend to be much smaller (averaging between 1–2 kb (kilobases) with fewer and smaller introns. Second, as we shall see in the following chapters, plant transcripts retain introns more often than do animal transcripts (30% of all genes in the model plant, Arabidopsis, compared to 10% in humans). Unfortunately, at this time we have only a few plant models for gene regulation, and only Arabidopsis, rice and poplar have been fully sequenced. Since Arabidopsis was the first plant genome to be fully sequenced, most of our information has come from studies of its transcriptome, and it is not known to what extent it truly represents other members of the plant kingdom. In addition, as our knowledge of factors influencing gene expression increases, so too, does our recognition that the current annotations in the gene databases will need to be updated to reflect new information as it appears in the literature. Finally, compared to animals, plants have evolved different signaling mechanisms, partly because plant hormones do not exactly function as do those in animals, and partly because plants must cope with environmental changes differently than animals, since they cannot physically escape their environments except possibly through reproduction. Therefore, plants have evolved very complex, interacting signaling pathways in response to developmental signals and biotic/abiotic stresses. All of these observations ultimately reflect some of the differences plants display in regulating gene expression compared to yeasts, insects and vertebrates. Although we have touched upon some of the differences between animal and plant control of gene expression here, it is equally important to recognize and appreciate the common mechanisms they share. For example, the basic transcriptional machinery via DNA-dependent RNA Polymerase II is virtually the same in plants and animals. Furthermore, some transcription factors, like myb and myc factors are similar in structure and function in both plants and animals. Plants and animals contain introns separating the coding regions of most genes and again, they utilize similar machinery to process the introns and form mature mRNAs. Since translation in all eukaryotes is basically the same, we see more similarities between plants and animals in this process, than differences. These mechanisms relate to mRNA structure, including sequences in the 5′ leader region and those in the 3′ untranslated region which influence the efficiency and selectivity of translation. It is hoped that the following chapters will expose the reader to some of the most recent, novel and fascinating examples of transcriptional and posttranscriptional control of gene expression in plants and, where appropriate, provide comparison to notable examples of animal gene regulation.