Expression of the tobacco Ext 1.4 extensin gene upon mechanical constraintand localization of regulatory regions

The regulation of the Ext 1.4 gene encoding a tobacco (Nicotiana tabacum L. ) extensin was studied in response to mechanical constraints, Transgenic pl ants carrying chimeric Ext 1.4 promoter/GUS (beta -glucuronidase)/nos termi nator or Ext 1.4 3'-end constructs were obtained. Expression of gene fusion s was found in tissues where mechanical stresses occur, e.g., during germin ation, as well as in root and stem tissues. Chimeric genes were successivel y and transiently expressed in different tissues during germination, i.e., at the tip of the root and then in the hypocotyl, during their growth throu gh the seed coat. Moreover, they were expressed in cortical cells surroundi ng the emergence of adventitious and lateral roots and developmentally-regu lated in nodes. The expression of Ext 1.4 could be induced by imposing. mec hanical constraints due to curving of either the stems or roots. Expression then occurred in cells where it does not normally occur, i.e., in cortical cells of internodes and in the distal piliferous zone of roots. Accumulati on of RNAs occurs several days after the start of the constraint. Promoter regions involved in regulation of expression of Ext 1.4 in stems, roots, an d in seedlings upon mechanical constraint could be localized. Moreover, the 3' non-coding region was shown to modulate expression in roots. These resu lts suggest that the regulation of Ext 1.4 following mechanical stress is d ependent on both tissue-specific and mechanical-responsive elements.