, 2009). In this work, we show that click here the use of functional genes, as the bacterial LmPH gene, as a proxy to study microbial diversity of relevant microorganisms in leaf litter decomposition is possible. We are confident that the use of other functional genetic markers

of bacteria, and its extension to the study of fungi, will provide additional and interesting results to support the idea of changing microbial communities in the process of litter decomposition and increase our understanding of how microorganism interacts in ecosystem processes. The authors acknowledge the contribution of Anna Díez to laboratory work. This research was financially supported by the Spanish Government through projects CGL2009-08338 and CGL2011-30151-C02-01. “
“hrp genes encode components of a type III secretion (T3S) system and play crucial roles in the pathogenicity of the rice pathogen Xanthomonas oryzae pv. oryzae (Xoo).

A histone-like nucleoid-structuring (H-NS) protein binds DNA and acts as a global PLX-4720 cost transcriptional repressor. Here, we investigated the involvement of an h-ns-like gene, named xrvB, in the expression of hrp genes in Xoo. Under the hrp-inducing culture condition, the expression of a key hrp regulator HrpG increased in the XrvB mutant, followed by activation of the downstream gene expression. Also, in planta, the secretion of a T3S protein (XopR) was activated

by the mutation in xrvB. Gel retardation assay indicated that XrvB has DNA-binding activity, but without a preference for the promoter region of hrpG. The results suggest that XrvB negatively regulates hrp gene expression and that an unknown factor(s) mediates the regulation of hrpG expression by XrvB. Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of bacterial leaf blight of rice (Swings et al., 1990; Niño-Liu et al., 2006). Like other Gram-negative phytopathogenic bacteria in the genera Erwinia, Pseudomonas, Ralstonia and Xanthomonas, Xoo possesses hypersensitive response and pathogenicity (hrp) genes, which play critical roles in conferring pathogenicity on host plants and triggering a hypersensitive response in nonhost plants (Alfano & Collmer, 1997). The hrp genes are involved in the construction why of a type III secretion (T3S) apparatus, through which bacterial virulence-associated proteins (effectors) are directly delivered into plant cells (Büttner & Bonas, 2002). The expression of hrp genes is tightly regulated and is induced in planta, but suppressed in complex media. Appropriate hrp-inducing media have been established for several bacteria; the media are generally nutrient poor and likely to mimic plant conditions (Schulte & Bonas, 1992; Xiao et al., 1992; Wengelnik et al., 1996a; Brito et al., 1999; Tsuge et al., 2002).