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An Erwinia amylovora inducible promoter for intragenic improvement of apple fire blight resistance
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International audience. Intragenesis is an important alternative to transgenesis to produce modified plants 27 containing native DNA only. A key point to develop such a strategy is the availability of 28 regulatory sequences controlling the expression of the gene of interest. With the aim of 29 finding apple gene promoters either inducible by the fire blight pathogen Erwinia amylovora 30 (Ea) or moderately constitutive, we focused on polyphenoloxidase genes (PPO). These genes 31 encode oxidative enzymes involved in many physiological processes and have been 32 previously shown to be up-regulated during the Ea infection process. We found ten PPO and 33 two PPO-like sequences in the apple genome and characterized the promoters of MdPPO16 34 (pPPO16) and MdKFDV02 PPO-like (pKFDV02) for their potential as Ea-inducible and low-35 constitutive regulatory sequences respectively. Expression levels of reporter genes fused to 36 these promoters and transiently or stably expressed in apple were quantified after various 37 treatments. Unlike pKFDV02 which displayed a variable activity, pPPO16 allowed a fast and 38 strong expression of transgenes in apple following Ea infection in a Type 3 Secretion System 39 dependent manner. Altogether our results indicate that pKFDV02 did not keep its promises as 40 a constitutive and weak promoter whereas pPPO16, the first Ea-inducible promoter cloned 41 from apple, can be a useful component of intragenic strategies to create fire blight resistant 42 apple genotypes.
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