Activation of three pathogen-inducible promoters of tobacco in transgenic pear (Pyrus communis L.) after abiotic and biotic elicitation.

In order to improve pear resistance against fire blight caused by Erwinia amylovora, a search for promoters driving high-level expression of transgenes specifically in response to this bacterial pathogen has been undertaken. We have examined the ability of hsr203J, str246C and sgd24 tobacco (Nicotiana tabacum L.) promoters to drive expression of the uidA reporter gene in pear. Transgenic pear clones were obtained by Agrobacterium tumefaciens-mediated transformation. Beta-glucuronidase activity was determined quantitatively and qualitatively in these plants grown in vitro using fluorometric and histochemical assays and compared to cauliflower mosaic virus (CaMV) 35S promoter-driven activity. The hsr203J promoter appeared to be very weakly activated following inoculation in pear, which is the converse of the situation in tobacco. The str246C promoter was rapidly activated in pear during compatible and incompatible interactions, by wounding and following the application of several elicitors (capsicein, cryptogein, harpin, salicylic acid and jasmonic acid). The sgd24 promoter, a deletion derivative of str246C, exhibited a low level of expression after bacterial inoculation, was weakly activated by wounding and elicitors, and was not activated by phytohormones (salicylic acid and jasmonic acid). Interestingly, the sgd24 promoter was locally activated in pear, whereas the str246C promoter was activated systemically from the infection site. Taken together, these data show that, although the s tr246C and sgd24 promoters are less active than the CaMV35S promoter in pear, their pathogen-responsiveness would permit them to be used to drive the expression of transgenes to promote bacterial disease resistance.