Identification of Novel Type III Secretion Effectors in Xanthomonas oryzae pv. oryzae

Abstract

Many gram-negative bacteria secrete so-called effector proteins via a type III secretion (T3S) system. Through genome screening for genes encoding potential T3S effectors, 60 candidates were selected from rice pathogen Xanthomonas oryzae pv. oryzae MAFF311018 using these criteria: i) homologs of known T3S effectors in plant-pathogenic bacteria, ii) genes with expression regulated by hrp regulatory protein HrpX, or iii) proteins with N-terminal amino acid patterns associated with T3S substrates of Pseudomonas syringae. Of effector candidates tested with the Bordetella pertussis calmodulin-dependent adenylate cyclase reporter for translocation into plant cells, 16 proteins were translocated in a T3S system-dependent manner. Of these 16 proteins, nine were homologs of known effectors in other plant-pathogenic bacteria and seven were not. Most of the effectors were widely conserved in Xanthomonas spp.; however, some were specific to X. oryzae. Interestingly, all these effectors were expressed in an HrpX-dependent manner, suggesting coregulation of effectors and the T3S system. In X. campestris pv. vesicatoria, HpaB and HpaC (HpaP in X. oryzae pv. oryzae) have a central role in recruiting T3S substrates to the secretion apparatus. Secretion of all but one effector was reduced in both HpaB() and HpaP() mutant strains, indicating that HpaB and HpaP are widely involved in efficient secretion of the effectors.

Xanthomonas oryzae pv. oryzae Type III Effector XopN Targets OsVOZ2 and a Putative Thiamine Synthase as a Virulence Factor in Rice

“…Nine non-TAL effectors have been identified in the Chinese strain 13751, among which XopR 13751 has been shown to affect virulence in Xoo [43]. In the present study, we chose XopN KXO85 to evaluate functional roles in the KXO85 strain and confirmed that it is secreted in an Hrp T3SS-dependent manner, translocated into the plant cytoplasm, and that its gene expression is regulated by HrpX KXO85 , as reported previously for other Xoo strains [13]. Among the Xop homologs in KXO85, we found that XopN KXO85 is the most critical for Xoo virulence in the Korean strain KXO85.…”

“…The T3SS of plant pathogenic species of Pseudomonas , Xanthomonas , Erwinia , and Ralstonia is highly conserved and involved in translocation of T3SS-dependent effector proteins from bacterial cells into plant cells [7–12]. These effector proteins are categorized into two groups: transcription activator-like (TAL) effectors and non-TAL effectors [11,13–15]. In Xoo , T3SS that is essential for virulence is encoded by hypersensitive response and pathogenicity (hrp) genes, the expression of which is controlled by HrpX [13,16,17].…”

“…These effector proteins are categorized into two groups: transcription activator-like (TAL) effectors and non-TAL effectors [11,13–15]. In Xoo , T3SS that is essential for virulence is encoded by hypersensitive response and pathogenicity (hrp) genes, the expression of which is controlled by HrpX [13,16,17]. …”

HpaB-Dependent Secretion of Type III Effectors in the Plant Pathogens Ralstonia solanacearum and Xanthomonas campestris pv. vesicatoria

“…Several studies in Xanthomonas spp. demonstrated that HpaB is important for T3E secretion/translocation 27, 28, 47, 48 . In Xanthomonas axonopodis pv.…”

Suppression of Rice Immunity by Xanthomonas oryzae Type III Effector Xoo2875

“…Bacteria growth in planta was measured as reported previously. 26) To analyze bacterial growth, inoculated rice leaves (length 1 cm) were collected at 5 dpi. Leaves were ground in and diluted with sterile water, then plated on a peptone-sucrose medium containing rifampicin and kanamycin to count bacterial numbers.…”