Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 3, 1999
Publication Date: N/A
Technical Abstract: Expression of genes in genetically modified alfalfa requires gene promoters that regulate the inserted genes in a desired spatial and temporal pattern. Although a wide variety of promoters have been described from crop species, few have been tested for use in alfalfa. Using the beta-glucuronidase (GUS) reporter gene, we have characterized the expression patterns in transgenic alfalfa of several nominally strong constitutive promoters, a number of alfalfa gene promoters, and several inducible promoters from heterologous species. The 35S promoter from the cauliflower mosaic virus is highly expressed in most cells of many crop plants. GUS activity in alfalfa leaves driven by the 35S promoter is 10- to 30-fold lower on a total leaf protein basis compared to activity in tobacco and Arabidopsis leaves, and we have observed rapid declines in GUS activity in alfalfa leaves of some plants as plants become more mature. Promoters tested from heterologous plants have not demonstrated the same tissue specificity or level of expression as found in the original plant species. In alfalfa the Arabidopsis class III chitinase promoter lacks root-enhanced activity seen in Arabidopsis but is active in phloem and cambial cells of vascular tissues and is inducible by fungal pathogen infection. The potato protease inhibitor II (pin2) promoter has low constitutive activity in vascular tissues, root tips, and leaf mesophyll in alfalfa. Upon wounding leaves, GUS activity in leaves increases 2- to 3-fold over 24 hours. We have characterized a number of tissue-specific and inducible promoters that are suited for expressing new traits in alfalfa, although additional strong constitutive promoters are needed for biotechnology applications.