HpaP divergently regulates the expression of hrp genes in Xanthomonas oryzae pathovars oryzae and oryzicola

Abstract

The bacterial pathogens Xanthomonas oryzae pathovars oryzae (Xoo) and oryzicola (Xoc) cause leaf blight and leaf streak diseases on rice, respectively. Pathogenesis is largely defined by the virulence genes harboured in the pathogen genome. Recently, we demonstrated that the protein HpaP of the crucifer pathogen Xanthomonas campestris pv. campestris is an enzyme with both ATPase and phosphatase activities, and is involved in regulating the synthesis of virulence factors and the induction of the hypersensitive response (HR). In this study, we investigated the role of HpaP homologues in Xoo and Xoc. We showed that HpaP is required for full virulence of Xoo and Xoc. Deletion of hpaP in Xoo and Xoc led to a reduction in virulence and alteration in the production of virulence factors, including extracellular polysaccharide and cell motility. Comparative transcriptomics and reverse transcription‐quantitative PCR assays revealed that in XVM2 medium, a mimic medium of the plant environment, the expression levels of hrp genes (for HR and pathogenicity) were enhanced in the Xoo hpaP deletion mutant compared to the wild type. By contrast, in the same growth conditions, hrp gene expression was decreased in the Xoc hpaP deletion mutant compared to the wild type. However, an opposite expression pattern was observed when the pathogens grew in planta, where the expression of hrp genes was reduced in the Xoo hpaP mutant but increased in the Xoc hpaP mutant. These findings indicate that HpaP plays a divergent role in Xoo and Xoc, which may lead to the different infection strategies employed by these two pathogens.

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“…actinidiae ( 93 ). Recently, Li et al ( 94 ) reported similar results in XVM2 medium, where the expression of hrp genes was decreased in Xanthomonas campestris pv. campestris ( Xcc ) hpaP deletion mutant.…”

The Transcriptional Regulator TfmR Directly Regulates Two Pathogenic Pathways in Xanthomonas oryzae pv. oryzicola

“…HR was tested on Nicotiana benthamiana leaves, as previously described [ 5 ]. Following a similar procedure, Xoc cells from cultures were washed and resuspended in sodium phosphate buffer (SPB, 5.8 mM Na 2 HPO 4 and 4.2 mM NaH 2 PO 4 , pH 7.0) to an OD 600 of 0.5 (5 × 10 8 CFU/mL).…”

“…Extracellular-polysaccharide (EPS) and extracellular-enzyme assays were conducted, following previously established protocols [ 4 , 5 ]. For EPS production analysis, the Xoc strain was spotted on NA plates supplemented with 2% sucrose and incubated for 3 days.…”

“…In recent years a large number of Xoc virulence factors have been identified and characterized. Xoc has been shown to produce and secrete a number of factors to promote its pathogenicity, including the extracellular polysaccharide (EPS), adhesion, diffusible signal factor (DSF) cell–cell signals, extracellular enzymes, and type III effectors (T3SEs) secreted through the type III secretion system (T3SS) et al [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. However, the molecular mechanisms that underpin the regulation of these virulence factors in Xoc are less explored and understood.…”

“…However, the molecular mechanisms that underpin the regulation of these virulence factors in Xoc are less explored and understood. Currently, the main pathogenic pathogenesis-related genes that have been identified in Xoc include the rpf gene and the T3SS gene, among others [ 5 , 6 ].…”