Mutations in the Predicted Active Site of Xanthomonas oryzae pv. oryzae XopQ Differentially Affect Virulence, Suppression of Host Innate Immunity, and Induction of the HR in a Nonhost Plant

Abstract

Xanthomonas oryzae pv. oryzae, the bacterial blight pathogen of rice, secretes a number of effectors through a type 3 secretion system. One of these effectors, called XopQ, is required for virulence and suppression of rice innate immune responses induced by the plant cell-wall-degrading enzyme lipase/esterase A (LipA). Bioinformatic analysis suggested that XopQ is homologous to inosine-uridine nucleoside hydrolases (NH). A structural model of XopQ with the protozoan Crithidia fasciculata purine NH suggested that D116 and Y279 are potential active site residues. X. oryzae pv. oryzae xopQ mutants (xopQ-/pHM1::xopQD116A and xopQ-/pHM1::xopQY279A) show reduced virulence on rice compared with xopQ-/pHM1::xopQ. The two predicted XopQ active site mutants (xopQ-/pHM1::xopQD116A and xopQ-/pHM1::xopQY279A) exhibit a reduced hypersensitive response (HR) on Nicotiana benthamiana, a nonhost. However, Arabidopsis lines expressing either xopQ or xopQY279A are equally proficient at suppression of LipA-induced callose deposition. Purified XopQ does not show NH activity on standard nucleoside substrates but exhibits ribose hydrolase activity on the nucleoside substrate analogue 4-nitrophenyl β-D-ribofuranoside. The D116A and Y279A mutations cause a reduction in biochemical activity. These results indicate that mutations in the predicted active site of XopQ affect virulence and induction of the HR but do not affect suppression of innate immunity.

Loss of chloroplast‐localized protein phosphatase 2Cs in Arabidopsis thaliana leads to enhancement of plant immunity and resistance to Xanthomonas campestris pv. campestris infection

“…Although the genome sequence of Xcc MAFF106712 is not available so far, it harbours at least XopN, XopK, XopQ, XopZ and XopR (Akimoto‐Tomiyama et al ., ). Single mutations of XopN, XopQ, XopZ (Cheong et al ., ; Gupta et al ., ; Song and Yang, ) and XopR (Akimoto‐Tomiyama et al ., ) have already been reported to affect virulence. Further analysis is needed to determine the T3E(s) involving PP2C expression and those T3Es with the potential to attenuate photosynthesis.…”

“…Many Xop proteins have been identified (Furutani et al, 2009) and characterized. The functions of XopR, XopN, XopZ, XopD, XopY, XopP, XopQ, AvrAC and AvrBs2 have been reported to be essential for bacterial virulence (Akimoto-Tomiyama et al, 2012;Cheong et al, 2013;Gupta et al, 2015;Ishikawa et al, 2014;Li et al, 2015;Song and Yang, 2010;Wang et al, 2015).…”

Xanthomonas axonopodis pv. punicae uses XopL effector to suppress pomegranate immunity

“…The results showed more callose deposition on leaves inoculated with Xap Δ xopL . Many Xop TTSS‐effectors are known to play a role in the suppression of PTI through reduced callose deposition, including XopQ of Xoo, XopJ of Xcv, XopN of Xap, XopD of Xcv (Kim et al ; Bartetzko et al ; Gupta et al ; Kumar et al ).…”

Overexpression of a cell wall damage induced transcription factor, OsWRKY42, leads to enhanced callose deposition and tolerance to salt stress but does not enhance tolerance to bacterial infection

“…After 16–18 h, the infiltrated region was cut and ground in liquid nitrogen followed by homogenization in lysis buffer (50 mM Tris-HCl [pH 7.5], NaCl [150 mM], Mannitol [250 mM], EDTA [5 mM], 10% Glycerol, 1 mM DTT 1% TritonX100, 1 mM PMSF, 1 mM NaF) with plant protease inhibitor cocktail (Sigma-Aldrich) [42]. Total protein supernatants were isolated after centrifugation at 15000 g for 15 min at 4 °C to remove cellular debris.…”