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Legume plants interact with rhizobia to form nitrogen-fixing root nodules. Legume-rhizobium interactions are specific and only compatible rhizobia and plant species will lead to nodule formation. Even within compatible interactions, the genotype of both the plant and the bacterial symbiont will impact on the efficiency of nodule functioning and nitrogen-fixation activity. The model legume Medicago truncatula forms nodules with several species of the Sinorhizobium genus. However, the efficiency of these bacterial strains is highly variable. In this study, we compared the symbiotic efficiency of Sinorhizobium meliloti strains Sm1021, 102F34, and FSM-MA, and Sinorhizobium medicae strain WSM419 on the two widely used M. truncatula accessions A17 and R108. The efficiency of the interactions was determined by multiple parameters. We found a high effectiveness of the FSM-MA strain with both M. truncatula accessions. In contrast, specific highly efficient interactions were obtained for the A17-WSM419 and R108-102F34 combinations. Remarkably, the widely used Sm1021 strain performed weakly on both hosts. We showed that Sm1021 efficiently induced nodule organogenesis but cannot fully activate the differentiation of the symbiotic nodule cells, explaining its weaker performance. These results will be informative for the selection of appropriate rhizobium strains in functional studies on symbiosis using these M. truncatula accessions, particularly for research focusing on late stages of the nodulation process.

The formation of symbiotic nodule cells in Medicago truncatula is driven by successive endoreduplication cycles and transcriptional reprogramming in different temporal waves including the activation of more than 600 cysteine-rich NCR genes expressed only in nodules. We show here that the transcriptional waves correlate with growing ploidy levels and have investigated how the epigenome changes during endoreduplication cycles. Differential DNA methylation was found in only a small subset of symbiotic nodule-specific genes, including more than half of the NCR genes, whereas in most genes DNA methylation was unaffected by the ploidy levels and was independent of the genes' active or repressed state. On the other hand, expression of nodule-specific genes correlated with ploidy-dependent opening of the chromatin as well as, in a subset of tested genes, with reduced H3K27me3 levels combined with enhanced H3K9ac levels. Our results suggest that endoreduplication-dependent epigenetic changes contribute to transcriptional reprogramming in the differentiation of symbiotic cells., Competing Interests: The authors declare no conflict of interest.

Propionibacterium acnes is an anaerobic Gram-positive bacterium that forms part of the normal human cutaneous microbiota and is thought to play a central role in acne vulgaris, a chronic inflammatory disease of the pilosebaceous unit (I. Kurokawa et al., Exp. Dermatol. 18:821-832, 2009). Here we present the whole genome sequence of P. acnes type IB strain 6609, which was recovered from a skin sample from a woman with no recorded acne history and is thus considered a nonpathogenic strain (I. Nagy, Microbes Infect. 8:2195-2205, 2006).

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases, affecting approximately one in 10,000 live births and with a carrier frequency of approximately one in 35. The disease is caused by a deficiency of the ubiquitous protein survival of motor neuron (SMN), which is encoded by the SMN1 and SMN2 genes. Due to a single nucleotide polymorphism in exon 7, SMN2 produces less full-length transcript than SMN1 and cannot prevent neuronal cell death at physiologic gene dosages. On the other hand, the copy number of SMN2 affects the amount of SMN protein produced and the severity of the SMA phenotype. SMN gene dosage analysis can determine the copy number of SMN1 to detect carriers and patients heterozygous for the absence of SMN1 exon 7. This study provides copy number estimation of SMN1 gene by real-time PCR technique in 56 SMA type I., II., III. patients, 159 parents and healthy relatives and in 152 undefined SMA patients. Among the family members, 91 carriers have been detected and in 56 patients homozygous deletion of SMN1 exon 7 has been confirmed. Moreover, in 12 patients compound heterozygosity of SMN1 exon 7 mutation has been detected, thus providing the possible diagnosis of SMA. In 94 patients, copy number of SMN2 has also been evaluated and a good correlation has been found with the phenotype of the disease. Due to the genetic complexity and the high carrier frequency, accurate risk assessment and genetic counselling are particularly important for the families. These new results provide improvement of the diagnostic service in SMA in Hungary with focus on proper genetic counselling and possible enrolment of the patients in future therapeutic interventions.