DEVELOPMENTAL AND PATHOGEN-INDUCED ACTIVATION OF AN MSR GENE, STR246C, FROM TOBACCO INVOLVES MULTIPLE REGULATORY ELEMENTS

A family of genes, the so-called msr genes (multiple stimulus response ), has recently been identified on the basis of sequence homology in v arious plant species. Members of this gene family are thought to be re gulated by a number of environmental or developmental stimuli, althoug h it is not known whether any one member responds more specifically to one stimulus, or whether each gene member responds to various environ mental stimuli. In this report, we address this question by studying t he tobacco msr gene str246C. Using transgenic tobacco plants containin g 2.1 kb of 5' flanking DNA sequence from the str246C gene fused to th e beta-glucuronidase (GUS) coding region, the complex expression patte rn of the str246C promoter has been characterized. Expression of the s tr246C promoter is strongly and rapidly induced by bacterial, fungal a nd viral infection and this induction is systemic. Elicitor preparatio ns from phytopathogenic bacteria and fungi activate the str246C promot er to high levels, as do wounding, the application of auxin, auxin and cytokinin, salicylic acid or copper sulfate, indicating the absence o f gene specialization within the msr gene family, at least for str246C . In addition, GUS activity was visualized histochemically in root mer istematic tissues of tobacco seedlings and is restricted to roots and sepals of mature plants. Finally, analysis of a series of 5' deletions of the str246C promoter-GUS gene fusion in transgenic tobacco plants confirms the involvement of multiple regulatory elements. A region of 83 bp was found to be necessary for induction of promoter activity in response to Pseudomonas solanacearum, while auxin inducibility and roo t expression are apparently not controlled by this element, since its removal does not abolish either response. An element of the promoter w ith a negative effect on promoter activation by P. solanacearum was al so identified.