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Xanthomonas albilineans OmpA1 Appears to be Functionally Modular and Both the OMC and C-like Domains Are Necessary for Leaf Scald Disease of Sugarcane

October 2013 , Volume 26 , Number  10
Pages  1,200 - 1,210

Laura A. Fleites,1 Imène Mensi,2 Daniel Gargani,2 Shujian Zhang,1 Philippe Rott,2 and Dean W. Gabriel1

1Department of Plant Pathology, University of Florida, Gainesville 32605, U.S.A.; 2CIRAD, UMR BGPI, F-34398 Montpellier, France

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Accepted 28 May 2013.

Several EZ-Tn5 insertions in gene locus XALc_0557 (OmpA1) of the sugarcane leaf scald pathogen Xanthomonas albilineans XaFL07-1 were previously found to strongly affect pathogenicity and endophytic stalk colonization. XALc_0557 has a predicted OmpA N-terminal outer membrane channel (OMC) domain and an OmpA C-like domain. Further analysis of mutant M468, with an EZ-Tn5 insertion in the upstream OMC domain coding region, revealed impaired epiphytic and endophytic leaf survival, impaired resistance to sodium dodecyl sulfate (SDS), structural defects in the outer membrane (OM), and hyperproduction of OM vesicles. Cloned full-length XALc_0557 complemented M468 for all phenotypes tested, including pathogenicity, resistance to SDS, and ability to survive both endophytically and epiphytically. Another construct, pCT47.3, which expressed only the C-like domain of XALc_0557, restored resistance to SDS in M468 but failed to complement any other mutant phenotype, indicating that the C-like domain functioned independently of the OMC domain to help maintain OM integrity. pCT47.3 also complemented pathogenicity, resistance to SDS, and stalk colonization in mutant M1152, which carries an EZ-Tn5 insert in the C-like coding region, indicating that both predicted domains are modular and necessary but neither is sufficient for X. albilineans pathogenicity, endophytic survival in, and epiphytic survival on sugarcane.

© 2013 The American Phytopathological Society