Tissue-Specific and Pathogen-lnduced Regulation of a Nicotiana plumbaginifolia

The Nicotiana plumbaginifolia gnl gene encoding a 8-1,3-glucanase isoform has been characterired. The gnl product represents an isoform distinct from the previously identified tobacco 8-1,3-glucanases. By expressing gnl in Escherichia coli, we have determined directly that the encoded protein does, indeed, correspond to a &1,3glucanase. In N. plumbaginifolia, gnl was found to be expressed in roots and older leaves. Transgenic tobacco plants containing the 5‘-noncoding region of gnl fused to the 8-glucuronidase (GUS) repotter gene also showed maximum levels of GUS activity in roots and older leaves. No detectable activity was present in the upper part of the transgenic plants with the exception of stem cells at the bases of emerging shoots. The expression conferred by the gnl promoter was differentially induced in response to specific plant stress treatments. Studies of three plant-bacteria interactions showed high levels of GUS activity when infection resulted in a hypersensitive reaction. lncreased gene expression was confined to cells surrounding the necrotic lesions. The observed expression pattern suggests that the characterized ,í3-1,3-glucanase plays a role both in plant development and in the defense response against pathogen infection.