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

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) is spread systemically through the xylem tissue and causes bacterial blight in rice. We evaluated the roles of Xanthomonas outer proteins (Xop) in the Xoo strain KXO85 in a Japonica-type rice cultivar, Dongjin. Five xop gene knockout mutants (xopQ KXO85, xopX KXO85, xopP1 KXO85, xopP2 KXO85, and xopN KXO85) were generated by EZ-Tn5 mutagenesis, and their virulence was assessed in 3-month-old rice leaves. Among these mutants, the xopN KXO85 mutant appeared to be less virulent than the wild-type KXO85; however, the difference was not statistically significant. In contrast, the xopN KXO85 mutant exhibited significantly less virulence in flag leaves after flowering than the wild-type KXO85. These observations indicate that the roles of Xop in Xoo virulence are dependent on leaf stage. We chose the xopN gene for further characterization because the xopN KXO85 mutant showed the greatest influence on virulence. We confirmed that XopNKXO85 is translocated into rice cells, and its gene expression is positively regulated by HrpX. Two rice proteins, OsVOZ2 and a putative thiamine synthase (OsXNP), were identified as targets of XopNKXO85 by yeast two-hybrid screening. Interactions between XopNKXO85 and OsVOZ2 and OsXNP were further confirmed in planta by bimolecular fluorescence complementation and in vivo pull-down assays. To investigate the roles of OsVOZ2 in interactions between rice and Xoo, we evaluated the virulence of the wild-type KXO85 and xopN KXO85 mutant in the OsVOZ2 mutant line PFG_3A-07565 of Dongjin. The wild-type KXO85 and xopN KXO85 mutant were significantly less virulent in the mutant rice line. These results indicate that XopNKXO85 and OsVOZ2 play important roles both individually and together for Xoo virulence in rice.

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.…”

The role of type III effectors from Xanthomonas axonopodis pv. manihotis in virulence and suppression of plant immunity

“…XopN has been reported to be an important virulence factor in other Xanthomonas spp. (Cheong et al, 2013;Jiang et al, 2008). It interacts with a 14-3-3 (TFT1) protein and with the Tomato Atypical Receptor-Like Kinase 1 (TARK1) in S. lycopersicum (Kim et al, 2009).…”

Xanthomonas vasicola pv. musacearum down-regulates selected defense genes during its interaction with both resistant and susceptible banana

“…Work in our laboratory has already shown that Xvm expressed HrpF (an indispensible gene for establishment of the type three secretion system) during infection of banana. Pathogen effectors are known to variously suppress host defence mechanisms [23] [24]. Repression of MbNBS below basal levels in the early hours following inoculation with Xvm therefore suggests that this pathogen causes its down regulation to evade detection (of its effectors).…”