Here, we report the presence of an acdS gene in M. ciceri UPM-Ca7T as well as in Mesorhizobium sp. MAFF303099. This result may be due c-Met inhibitor to the fact that a hybridization probe based on the acdS gene of Mesorhizobium sp. MAFF303099 was used in the present study, while in the study performed by Ma et al. (2003b), the probe was based on the P. putida UW4 acdS gene. This notwithstanding, similar Southern hybridization results were obtained with the Mesorhizobium sp. MAFF303099 strain, where the acdS gene is present on a ~ 6-kb fragment, as previously described by Ma et al. (2003b). Using the acdS gene of Mesorhizobium sp. MAFF303099 as a hybridization probe, acdS genes were detected in the 18 chickpea mesorhizobia isolates tested here. These

isolates belong to a collection that includes soil isolates from all over Portugal (Alexandre et al., 2009), indicating that many of the Portuguese chickpea Mesorhizobium possess an acdS gene and suggesting that ACC deaminase genes are prevalent in these chickpea-nodulating mesorhizobia. However, similar to the results obtained by Ma et al. (2003b) with M. ciceri UPM-Ca7T and Mesorhizobium sp. MAFF303099, ACC deaminase activity was not detected, under free-living conditions, in any of the Mesorhizobium strains tested. On the other hand, Uchiumi et al. (2004) demonstrated that Mesorhizobium

sp. MAFF303099, despite showing no ACC deaminase under free-living conditions, produces ACC deaminase in the bacteroid state, indicating that ACC deaminase is only produced under symbiotic conditions. Subsequent studies by Nukui et al. (2006) showed that ACC deaminase production by Mesorhizobium sp. MAFF303099 is under transcriptional Wnt inhibitor control of the

NifA2 protein. In the work reported here, RNA was extracted from M. ciceri UPM-Ca7T nodules, and after RT-PCR amplification, it was possible to detect the acdS transcript using Mesorhizobium acdS specific primers. This indicates that M. ciceri UPM-Ca7T also expresses its acdS gene under symbiotic conditions. In addition to the data of Uchiumi et al. (2004) and Nukui et al. (2006), this result suggests that ACC deaminase production under symbiotic conditions may occur in many Mesorhizobium strains. Moreover, analysis of the upstream regions of the acdS gene in M. loti R7A, Mesorhizobium sp. MAFF303099, M. ciceri bv. biserrulae WSM1271, M. australicum WSM2073T, and M. opportunistum WSM2075T indicate Oxaprozin a putative NifA UAS, suggesting that NifA regulation of acdS expression may be common within the Mesorhizobium genus. The acdS phylogenetic tree shows a topology similar to the symbiosis (nodC and nifH) genes-based trees (Figs 2 and 3; Laranjo et al., 2008), grouping isolates that nodulate the same host, rather than grouping by species as in the 16S rRNA gene-based phylogeny. Several studies show that many Mesorhizobium strains have acquired the ability to nodulate a specific host by acquiring a symbiosis island carrying specific symbiosis genes (Sullivan et al.