HrpE, the major component of the Xanthomonas type three protein secretion pilus, elicits plant immunity responses

• Published in: Scientific reports 2018-06, Vol.8 (1), p.9842-13, Article 9842
• Main Authors: Gottig, Natalia, Vranych, Cecilia V., Sgro, Germán G., Piazza, Ainelén, Ottado, Jorgelina
• Format: Article
• Language: English
• Subjects: 14; 14/19; 38; 38/77; 631/326/421; 631/449/2169/2674; 82; 82/111; 82/80; 82/83; 96; Arabidopsis; Host plants; Humanities and Social Sciences; Hydrogen peroxide; multidisciplinary; Pathogens; Plant immunity; Proteins; Science; Science (multidisciplinary); Tomatoes; Xanthomonas
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-27869-1

Like several pathogenic bacteria, Xanthomonas infect host plants through the secretion of effector proteins by the Hrp pilus of the T ype Three Protein S ecretion S ystem (T3SS). HrpE protein was identified as the major structural component of this pilus. Here, using the Xanthomonas citri subsp. citri ( Xcc ) HrpE as a model, a novel role for this protein as an elicitor of plant defense responses was found. HrpE triggers defense responses in host and non-host plants revealed by the development of plant lesions, callose deposition, hydrogen peroxide production and increase in the expression levels of genes related to plant defense responses. Moreover, pre-infiltration of citrus or tomato leaves with HrpE impairs later Xanthomonas infections. Particularly, HrpE C-terminal region, conserved among Xanthomonas species, was sufficient to elicit these responses. HrpE was able to interact with plant G lycine- R ich P roteins from citrus (CsGRP) and Arabidopsis (AtGRP-3). Moreover, an Arabidopsis a tgrp-3 knockout mutant lost the capacity to respond to HrpE. This work demonstrate that plants can recognize the conserved C-terminal region of the T3SS pilus HrpE protein as a danger signal to defend themselves against Xanthomonas, triggering defense responses that may be mediated by GRPs.