|SCHROPFER, SUSAN - Julius Kuhn Institute
|BOTTCHER, CHRISTOPH - Julius Kuhn Institute
|WOHNER, THOMAS - Julius Kuhn Institute
|RICHTER, KLAUS - Julius Kuhn Institute
|RIKKERINK, ERIK H.A - Plant And Food Research
|HANKE, MAGDA-VIOLA - Julius Kuhn Institute
|FLACHOWSKY, HENRYK - Julius Kuhn Institute
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2018
Publication Date: N/A
Interpretive Summary: Fire blight is a devastating bacterial disease of apple trees that results in severe economic losses. It is known that a specific protein produced by the fire blight bacteria, called AvrRpt2EA, is important for pathogen recognition in the fire blight resistant crabapple ‘Robusta 5’ which was used to develop several of the fire blight resistant ‘Geneva’ rootstocks. However, little is known about the role of this protein in susceptible apple varieties. In order to study the function of this protein we expressed AvrRpt2EA protein in fire blight susceptible ‘Pinova’ apple plants using a heat-inducible gene expression system. After the AvrRpt2EA protein was expressed in susceptible apple plants they developed symptoms similar to natural fire blight infections with browning leaves and death of vegetative shoots. Expression of the protein also resulted in increased levels of the plant hormone salicylic acid (SA) and the systemic acquired disease resistance pathway it controls. In contrast, no increased activation of the jasmonic acid (JA)-dependent defense pathway could be detected. Our work demonstrates that AvrRpt2EA protein acts as virulence factor and plays an important role in the antagonism between SA- and JA-signaling to facilitate the further colonization of the infected plant by the fire blight pathogen.
Technical Abstract: The AvrRpt2EA effector protein of Erwinia amylovora is important for pathogen recognition in the fire blight resistant crabapple Malus ×robusta 5; however, little is known about its role in susceptible apple genotypes. In order to study its function in planta, we expressed a plant optimized version of AvrRpt2EA driven by a heat-shock inducible promoter in transgenic plants of the fire blight susceptible apple cultivar 'Pinova'. After induced expression of AvrRpt2EA, transgenic lines showed shoot necrosis and browning of elderly leaves, with symptoms similar to natural fire blight infections. Transgenic expression of this bacterial effector protein resulted in an increase in the expression of the salicylic acid (SA)-responsive PR-1 gene, but also in the levels of SA and its derivatives with diverse kinetics in leaves of different age. In contrast, no increase of expression levels of VSP2 paralogs used as marker genes for the activation of the jasmonic acid (JA)-dependent defense pathway could be detected, which is in agreement with metabolic profiling of JA and its derivatives. Our work demonstrates that AvrRpt2EA acts as virulence factor and plays an important role in the antagonism between SA- and JA-signaling to facilitate the further colonization of the infected plant by the necrotrophic pathogen.