Identification of HrpX regulon genes in Xanthomonas oryzae pv. oryzicola using a GFP visualization technique
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ORIGINAL PAPER
IdentiWcation of HrpX regulon genes in Xanthomonas oryzae pv. oryzicola using a GFP visualization technique Yurong Li · Youlun Xiao · Lifang Zou · Huasong Zou · Gongyou Chen
Received: 26 June 2011 / Revised: 3 September 2011 / Accepted: 24 September 2011 / Published online: 11 October 2011 © Springer-Verlag 2011
Abstract Xanthomonas oryzae pv. oryzicola is the causal agent of bacterial leaf streak in rice and injects repertoires of T3S eVectors (T3SEs), which are normally regulated by a global regulator HrpX, into plant cells to suppress plant innate immunity for disease development. To establish a visualization technique to identify HrpX regulon genes in this pathogen, we chose six known or unknown T3SE genes of X. oryzae pv. oryzicola (strain RS105) as the targets in this report. The promoters of these candidates, whether or not containing a PIP-box, were fused with the gfp (green Xuorescent protein) reporter gene, and the gfp reporters were introduced into the wild-type RS105 and the hrpX mutant RhrpX. GFP expression in the wild-type strain could be observed under Xuorescence microscopy, but Xuorescence was not observed in the hrpX mutant. Consequently, transcription and secretion detection demonstrated that these HrpX regulon members were repressed when hrpX was mutated and were not secreted into the hrpinducing medium XOM3 because of a mutation in hrcV (T3SS deWcient). These data suggest that the gfp reporter system is a feasible visualization tool for the identiWcation of HrpX regulon genes and discovery of new T3SEs in the X. oryzae pv. oryzicola-rice pathosystem.
Communicated by Jorge Membrillo-Hernandez. Y. Li · L. Zou · H. Zou · G. Chen (&) Department of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China e-mail: [email protected] Present Address: Y. Xiao Institute of Plant Protection, Hunan Academy of Agricultural Sciences, 726 Yuanda Road, Changsha 410125, China
Keywords X. oryzae pv. oryzicola · HrpX regulon gene · gfp · PIP-box
Introduction Xanthomonas oryzae pv. oryzicola (Xoc), the causal agent of bacterial leaf streak (BLS) in rice (Oryza sativa), is emerging as an important pathogen and is a recognized biosecurity threat to rice-growing countries in addition to those in South Asia (Mew 1993; Staskawicz et al. 2001). The Xoc-rice pathosystem is a model as the X. oryzae pv. oryzae (Xoo)-rice pathosystem in identifying the molecular mechanisms of plant–pathogen interactions (Swings et al. 1990; Zou et al. 2006; Niño-Liu et al. 2006), particularly because Xoc invades rice through the stomata and grows among parenchymal tissues between the veins, whereas Xoo infects rice via hydathodes and multiplies in the vascular system. This mechanistic delineation assumes that the two pathovars are armed with diVerent tissue factors for their infection in rice (Zou et al. 2010). Similar to Xoo and other Gram-negative pathogenic bacteria in plants and animals, Xoc possesses a T3SS (type-III secretion system) encoded by hrp–hrc–hpa genes that determines its ability t
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