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Résumé du séminaire de Ralf Koebnik - IRD Montpellier UMR IPME


Microbe’s Life without SWEETs: TALEs from Xanthomonas

Bacterial Leaf Blight is amongst the most important diseases of rice. As a key virulence strategy to cause disease, bacteria of the species Xanthomonas oryzae inject into the plant cell DNA-binding proteins called Transcription Activator-Like Effectors (TALEs), that bind to Effector-Binding Elements (EBEs) in a sequence-specific manner, resulting in host gene induction. Different TALEs, found in geographically distant Xanthomonas oryzae strains, all induce the expression of the sugar transporter SWEET14, which is thus considered as a pivotal TALE target acting as major susceptibility factor. We will describe an allele library of SWEET14 promoter that was generated through stable expression of TALE-Nuclease (TALEN) constructs in rice. The susceptibility level of lines carrying mutations in three EBEs was assessed. Plants edited in two of the EBEs were resistant to bacterial strains relying on the corresponding TALE. Surprisingly, although indels within the third EBE prevented SWEET14 induction in response to bacteria relying on the corresponding TALE, loss of SWEET14 gene induction failed to confer resistance to this strain. This mutant rice line was, however, resistant to a strain expressing an artificial SWEET14-inducing TALE whose EBE was also edited in this line. This work uncovers a distinct, broader range of activities for the TALE TalC compared to other TALEs inducing SWEET14. We propose the existence of additional targets for this TALE beyond SWEET14, suggesting that TALE-mediated plant susceptibility may result from induction of several, genetically redundant, host susceptibility genes by a single effector.

 

 

asques et ascospores de Magnaporthe orizae - copyright : JL Notteghem spores Magnaporthe oryzae - copyright : JL Notteghem bactéries Xanthomonas pseudoalbilineans (gauche) et Xanthomonas albilineans (droite). Les deux produisent l'antibiotique albicidine (structure en haut de la photo - copyright : S. Cociancich/A. Mainz
  champignon Magnaporthe (vert) en train d'attaquer une feuille de riz - copyright : A. Delteil/JB Morel test d'anticorps sur puceron (Mysus persicae) - copyright : MS Vernerey/M. van Munster/M. Uzest