Determination of the role of HrpN effector protein, as a key factor in course of interaction between Erwinia amylovora w
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ORIGINAL ARTICLE
Determination of the role of HrpN effector protein, as a key factor in course of interaction between Erwinia amylovora with chloroplasts of pear (Pyrus communis L.) Azam Taheri Shahrestani 1 & Hamid Abdollahi 2 & Bagher Yakhchali 3 & Rahim Mehrabi 4 & Omid Eini Gandomani 1 Received: 21 January 2020 / Accepted: 21 August 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Abstract Fire blight caused by the gram-negative bacterium Erwinia amylovora is the most destructive disease of pome fruit trees. The pathogen induces the disease by secreting HrpN, HrpW, and DspA/E effector proteins into host tissues triggering oxidative burst. To study the role of these effectors in the course of interaction with host plants, hrpN−, hrpW− and dspA/E− mutants were inoculated on two pear cultivars under in situ (greenhouse and immature fruit) and in vitro systems. In addition, the determinantal role of these effectors on host chloroplasts was studied under activated and inactivated electron cascade of chloroplasts. Results showed that the lack of HrpN and DspA/E effectors postponed the initiation of necrosis and also decreased necrosis progress rate in comparison with the wild type strain. In contrast, hrpW− had the least decline in the pathogenicity of fire blight. The comparison of chloroplast activity confirmed the role of effectors in in situ experiments and also revealed that HrpN could be the main factor for the interaction of the pathogen with host cell chloroplasts. Keywords Chloroplast . Effector proteins . Electron transport chain . Fire blight . Systemic acquired resistance
Introduction Erwinia amylovora, the causal agent of fire blight disease, is a vascular necrosis pathogen in pome fruit trees such as pear and apple. During the last decades, genetic studies have resulted in revealing some aspects of molecular mechanisms underlying pathogenesis of fire blight (Khan et al. 2012). The bacterial virulence strongly depends on the production of effector proteins secreted through the type III secretion system and also the production of amylovoran exopolysaccharide (EPS) (Zhao and Qi 2011). Identification
* Azam Taheri Shahrestani [email protected] Hamid Abdollahi [email protected] Bagher Yakhchali [email protected]
of genes encoding effector proteins in the bacterium could be achieved through a targeted or random mutation approach. For example, Bellemann and Geider (1992) used mutant strains of E. amylovora in order to study genetic characters of ams gene cluster that is involved in amylovoran EPS production. Similarly, mutation of ams region by Tn3Gus insertion showed that alteration in EPS synthesis was correlated with the pathogenicity and reduced (or no) growth in planta (Menggad and Laurent 1998). It was found that amylovoran production in amyR knock out mutant was about eight-fold higher than that in the wild type strain (Wang et al. 2012),
1
Department of Plant Protection, Faculty of Agriculture, University of Zanjan, Zanjan, Iran
2
Temperate Fruits Research Centre, Horticul
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