Characterization of cDNAs differentially expressed in roots of tobacco (Nicotiana tabacum cv Burley 21) during the early stages of alkaloid biosynthesis

A set of 60 cDNAs were isolated by subtractive hybridization screening of a phage library using radioactively-labeled probes generated from root mRNAs isolated from tobacco (Nicotiana tabacum cv Burley 21) plants before and 3 days after topping. Among the differentially expressed gene products were full-length and partial cDNAs encoding arginine decarboxylase (ADC), ornith ine decarboxylase (ODC), and S-adenosylmethionine synthetase (SAMS), enzyme s involved in polyamine and alkaloid biosynthesis. The other cDNAs isolated were placed into one of several categories and encode metabolic enzymes, p roteins involved in transcription and translation, components of signal tra nsduction pathways, and homologs of genes whose expression has been shown t o be regulated by phytohormones (i.e. auxin, ABA), wounding or other stress responses. RNA gel blot analysis showed that the ADC and ODC transcripts w ere preferentially expressed in the roots and floral tissues of mature toba cco plants, whereas SAMS transcripts were detected in all tissues examined. The steady-state levels of the ADC and ODC mRNAs increased in the roots of wild-type tobacco plants during the 24 h period after topping, whereas lit tle change was observed in the abundance of the SAMS transcripts in these t issues. The possible factors associated with the regulation of expression o f these genes are discussed. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.