Characterization of a tobacco epoxide hydrolase gene induced during the resistance response to TMV.
A clone encoding a putative soluble epoxide hydrolase (EH-1), an enzyme which converts epoxides to diols, was isolated by differential screening of a cDNA library prepared from tobacco mosaic virus (TMV)-infected tobacco leaves. To confirm that EH-1 encodes an epoxide hydrolase, the recombinant EH-1 protein produced in bacteria was shown to have high epoxide hydrolase activity in vitro. Infection of resistant but not susceptible tobacco cultivars induced the accumulation of EH-1 transcripts in both the inoculated and uninoculated, systemic leaves. EH-1 expression was also induced in the inoculated and systemic tissues of TMV-infected NahG plants, which are unable to accumulate salicylic acid (SA). However, EH-1 expression in the inoculated leaves of NahG plants was delayed, whilst in the systemic leaves the induction was both later and weaker, compared to that observed in wild-type plants. Furthermore, exogenously applied SA or its functional analog 2,6-dichloroisonicotinic acid (INA) caused a rapid and transient accumulation of EH-1 transcripts, whereas an inactive SA analog did not. Thus, the induction of EH-1 gene expression appears to be regulated by both SA-independent and SA-dependent pathways. Since EH-1 was expressed only in TMV-resistant tobacco after infection, and the encoded enzyme is thought to help metabolize toxic compounds, we propose that EH-1 may play a role in protection from oxidative damage associated with defense responses. It may also play a role in generating signals for activation of certain defense responses.
Waksman Institute, Rutgers, State University of New Jersey, Piscataway 08855, USA.
A
A
Guo
J
J
Durner
D F
DF
Klessig
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D018744:DNA, Plant; D004790:Enzyme Induction; D004851:Epoxide Hydrolases / Q000235:genetics*; D004926:Escherichia coli; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007210:Indoleacetic Acids / Q000494:pharmacology; D007539:Isonicotinic Acids / Q000494:pharmacology; D008969:Molecular Sequence Data; D005810:Multigene Family; D010947:Plants, Toxic; D011994:Recombinant Proteins; D020156:Salicylic Acid / Q000494:pharmacology; D013696:Temperature; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics; D014027:Tobacco Mosaic Virus / Q000502:physiology; D014764:Viral Proteins
D018744:DNA, Plant; D007210:Indoleacetic Acids; D007539:Isonicotinic Acids; D011994:Recombinant Proteins; D014764:Viral Proteins; C077261:2,6-dichloroisonicotinic acid; D004851:Epoxide Hydrolases; C115143:EH-1 protein, Tobacco mosaic virus; D020156:Salicylic Acid