The activation sequence-1 (as-1)-like element found in the promoter of some glutathione S-transferase (GST) genes, has been previously described as a salicylic acid (SA)-and auxin-responsive element. In this paper, we tested the hypothesis that the activating effect of SA on the as-1 element is mediated by oxidative species. Supporting this hypothesis, our results show that the antioxidants dimethylthiourea (DMTU) and 3-t-butyl-4-hydroxy-anizole (BHA) inhibit the SA-induced transcription of genes controlled by as-1 elements in tobacco (Nicotiana tabacum) plants [i.e. GNT35 gene coding for a GST and (as-1) 4 /␤-glucuronidase (GUS) reporter transgene]. DMTU and BHA also inhibit SA-activated as-1-binding activity in nuclear extracts. Further support for the hypothesis that the as-1 element is activated by oxidative species comes from our result showing that light potentiates the SA-induced activation of the as-1 element. Furthermore, methyl viologen, a known oxidative stress inducer in plants, also activates the as-1 element. Increasing H 2 O 2 levels by incubation with H 2 O 2 or with the catalase inhibitor 3-amino-1,2,5-triazole does not activate the (as-1) 4 /GUS gene. On the contrary, 3-amino-1,2,5-triazole inhibits the activating effect of SA on the (as-1) 4 /GUS gene. These results suggest that oxidative species other than H 2 O 2 mediate the activation of the as-1 element by SA. Our results also suggest that even though the as-1 binding activity is stimulated by oxidative species, this is not sufficient for the transactivation of genes controlled by this element. The complex interplay between SA and reactive oxygen species in the transcriptional activation of defense genes is discussed.Salicylic acid (SA) is a phenolic hormone that plays a crucial role in stress resistance in plants (Durner et al., 1997; Alvarez, 2000). Cellular levels of SA increase in the onset of pathogen-induced defense reactions, locally in the infected tissues or systemically in noninfected tissues (Malamy et al., 1990). Increased levels of SA are required to activate the transcription of defense genes and to develop an efficient pathogen resistance response (Gaffney et al., 1993; Delaney et al., 1994). It is interesting that accumulation of SA and the activation of defense genes have been also reported to occur after exposure of plants to ozone or UV radiation (Yalpani et al., 1994;Rao and Davis, 1999). Pathogen infection and exposure to ozone or UV radiation are associated with an accumulation of reactive oxygen species (ROS) in plants. The appropriate balance in the cellular levels of SA and ROS seems to be crucial for the efficient activation of defense responses against the abovementioned environmental stressors (Draper, 1997;Van Camp et al., 1998; Alvarez, 2000;Van Breusegem et al., 2001).One class of defense genes activated by SA is the glutathione S-transferase (GST) class of genes that code for the GSTs. In plants, GSTs are key enzymes in the metabolism of xenobiotics and secondary products. They catalyze the formation of glu...

Trehalose has many potential applications in biotechnology and the food industry due to its protective effect against environmental stress. Our work explores microbiological production methods based on the capacity of Corynebacterium glutamicum to excrete trehalose. We address here raising trehalose productivity through homologous overexpression of maltooligosyltrehalose synthase and the maltooligosyltrehalose trehalohydrolase genes. In addition, heterologous expression of the UDP-glucose pyrophosphorylase gene from Escherichia coli improved the supply of glycogen. Gene expression effects were tested on enzymatic activities and intracellular glycogen content, as well as on accumulated and excreted trehalose. Overexpression of the treY gene and the treY/treZ synthetic operon significantly increased maltooligosyltrehalose synthase activity, the rate-limiting step, and improved the specific productivity and the final titer of trehalose. Furthermore, a strong decrease was noted in glycogen accumulation. Expression of galU/treY and galU/treYZ synthetic operons showed a partial recovery in the intracellular glycogen levels and a significant improvement in both intra-and extracellular trehalose content.Trehalose contains two glucose molecules linked by an ␣-1,1 glycosidic bond. It is a stable, odor-free, and nonreducing disaccharide widely found in nature (27). Its properties as a protein and cell stabilizer make the molecule a promising biotechnological additive for tissue and organ preservation, protein technology, and several food applications.Trehalose is currently synthesized on an industrial scale by using the method patented by Hayashibara Biochemical Laboratories (17, 18), which is based on direct transformation from maltodextrin using two enzymes obtained from the culture of Rhizobium sp. strain M11 or Arthrobacter sp. strain Q36.Our approach to production is microbiological and makes use of the fact that Corynebacterium glutamicum a gram-positive bacterium (15), excretes significant amounts of trehalose during batch cultures (29, 32). C. glutamicum has been used extensively for the industrial production of vitamins and numerous L-amino acids for foodstuffs (16).C. glutamicum uses three pathways in trehalose synthesis (28, 33): the TreS pathway, directly converting maltose into trehalose catalyzed by trehalose synthase (TreS) (5, 21); the OtsAB pathway, wherein trehalose synthesis starts from UDPglucose and glucose-6-phosphate and is catalyzed in two steps by trehalose-6-phosphate synthase (OtsA), followed by trehalose-6-phosphate phosphatase (OtsB); and the TreYZ pathway, in which enzymatic conversion of the ␣-glucan polymer into trehalose is catalyzed in two steps by maltooligosyltrehalose synthase (TreY) and maltooligosyltrehalose trehalohydrolase (TreZ), respectively. The regulatory mechanisms of each pathway remain unclear, and just how the three are interrelated is unknown. However, recent studies showed that under hyperosmotic conditions, osmoregulated trehalose synthesis in C. glutamicum is mediated by...