Ozone has dramatic effects on the regulation of the prechorismate pathway in tobacco (Nicotiana tabacum L. cv. Bel W3)

Abstract

The accumulation of aromatic secondary metabolites is a well-known element of the plant response to ozone. Most of these metabolites are synthesized via the three aromatic amino acids phenylalanine, tyrosine and tryptophan. Before branching, the biosynthetic pathway to the three amino acids shares seven enzymatic steps, called the prechorismate pathway, catalysed by 3-deoxy-D: -arabino-heptulosonate-7-phosphate (DAHP) synthase [EC 2.5.1.54], 3-dehydroquinate synthase [EC 4.2.3.4], 3-dehydroquinate dehydratase [EC 4.2.1.10]-shikimate 5-dehydrogenase [EC 1.1.1.25], shikimate kinase [EC 2.7.1.71], 5-enolpyruvylshikimate 3-phosphate synthase [EC 2.5.1.19] and chorismate synthase [EC 4.2.3.5]). We have studied the transcript level of these enzymes and the aromatic metabolite profile in the ozone sensitive tobacco cultivar BelW3 (Nicotiana tabacum L. cv Bel W3), when exposed to an acute ozone pulse (160 nl l(-1), 5 h). Specific cDNA-fragments of the corresponding six genes were isolated from tobacco Bel W3 and used as probes for determining the expression of the prechorismate pathway genes. The fully expanded leaves of ozone treated plants, which developed symptoms like necrotic leaf spots and accumulation of aromatic metabolites, showed a clear induction of the shikimate pathway genes; indicating, that this induction is linked to the development of the symptoms. Distinct kinetics and magnitudes were observed in tobacco leaves for the ozone dependent enhanced mRNA accumulation of the aforementioned genes in BelW3. The strongest and earliest induction due to ozone treatment could be observed for DAHP synthase. An isoform-specific analysis of the transcripts showed a strong induction on transcript level only for one of three isoforms, which was followed by the induction of the DAHP synthase also on protein level. The different induction kinetics of the prechorismate pathway genes indicate that their regulation in response to ozone might be regulated by different signals, for example, ethylene, reactive oxygen species or salicylic acid, which also occur with different kinetics and thus may play different roles in the plant response to ozone.

Overexpression of the Wounding‐Responsive Gene AtMYB15 Activates the Shikimate Pathway in Arabidopsis

“…48 No. 9 2006 in a coordinated manner in response to stresses (Henstrand et al 1992; Gorlach et al 1995;Janzik et al 2005). Interestingly, levels of At4g33510 (DHS2) and At1g48860 transcripts coding for isoforms of DAHP synthase and EPSP synthase, respectively, were not affected by wounding (Figure 5).…”

“…Shikimate pathway related genes were also found to be induced by light or fungal elicitors in parsley and tomato (Henstrand et al 1992;Gorlach et al 1995b). Recently, the effect of ozone on the expression of the shikimate pathway genes has been investigated in tobacco (Janzik et al 2005).…”

“…Shikimate pathway related genes were also found to be induced by light or fungal elicitors in parsley and tomato (Henstrand et al 1992;Gorlach et al 1995b). Recently, the effect of ozone on the expression of the shikimate pathway genes has been investigated in tobacco (Janzik et al 2005).In the present paper, we report on the identification and characterization of an R2R3-type MYB transcription factor (AtMYB15) as a nucleus-localized transcriptional activator of the shikimate pathway in Arabidopsis. The mRNA of AtMYB15 is rapidly induced by wounding and overexpression of AtMYB15 in transgenic Arabidopsis plants resulted in elevated expression of shikimate pathway genes.…”

“…Interestingly, two genes (one SK gene, At2g21940, and one EPSPS gene, At1g48860) that were not induced by wounding were found to be upregulated in AtMYB15-ox plants ( Figure 4C). It has been reported that ozone and pathogen elicitors are able to trigger extensive activation of shikimate pathway genes and many genes encoding enzymes of the shikimate pathway show tissue-specific expression patterns (Gasser et al 1988;Henstrand et al 1992;Gorlach et al 1995a;Janzik et al 2005;Kasai et al 2005). The fact that AtMYB15 overexpression was able to activate these two genes that were not wound inducible may also reflect the sophisticated action of AtMYB15 over different tissue types or in response to different stimuli.…”

Estudio transcriptómico de los mecanismos implicados en la tolerancia inducida por el curado al daño de frío y por el etileno al colapso de la corteza en los frutos cítricos.

“…En plantas, la inducción de procesos de biosíntesis de los aminoácidos aromáticos se ha relacionado con una necesidad de biosíntesis de nuevas proteínas y de metabolitos secundarios, alcaloides y fenilpropanoides, que actúan como componentes estructurales además de como reguladores del crecimiento y participan en las respuestas de defensa a la infección por patógenos, la herida u otros tipo de estrés, incluyendo el estrés oxidativo (Swain, 1977;Hashimoto y Yamada, 1994;Conn, 1995;Kutchan, 1995;Zhao et al, 1998). Se ha sugerido que su inducción en respuesta a situaciones de estrés podría estar regulada por diferentes señales, como el etileno, ROS o el ácido salicílico (Zhao et al, 1998;Janzik et al, 2005;Ogawa et al, 2005). En el flavedo de los frutos recién acondicionados con etileno se encontró una elevada representación de genes inducidos que participan en el metabolismo del triptófano y en procesos de biosíntesis de indolalquilaminas (Tabla 29A y Tabla 30).…”