IDENTIFICATION OF SINORHIZOBIUM MELILOTI GENES RELEVANT FOR THE COLONIZATION OF HOST PLANT ROOTS DURING THE EARLY STAGES OF THE SYMBIOTIC INTERACTION

LOZANO, MAURICIO JAVIER; SALAS, MARÍA EUGENIA; PARISI, GUSTAVO; LOPEZ, JOSÉ LUIS; ALBICORO, FRANCISCO JAVIER; MARTINI, MARÍA CARLA; SALTO, ILEANA PAULA; PISTORIO, MARIANO; DEL PAPA, MARÍA FLORENCIA; BECKER, ANKE; LAGARES, ANTONIO

Congreso; XVI International Congress on Molecular Plant-Microbe Interactions; 2014

Sinorhizobium meliloti is a gram-negative proteobacterium able to establish nitrogen-fixing symbiosis with legumes of the genera Medicago, Melilotus, and Trigonella. This association is tightly regulated, and rhizobial strains in the soil compete for the colonization of the symbiotic niche. Unfortunately, the molecular bases of the early competition are not fully understood yet, limiting the biotechnological improvement of inoculant strains. To discover new genes relevant for these early events we used two experimental approaches designed for the study of biological niches which cannot be easily replicated in vitro. Namely, Recombination-based In Vivo Expression Technology (RIVET) and Signature-Tagged Mutagenesis (STM). For the RIVET approach we generated a S. meliloti library of transcriptional fusions to tnpR (site-specific recombinase) and upon transferring it to the positive selection strain S. meliloti 2011R1ΩNGG (Lozano et al. 2011), we conducted several root colonization experiments using low numbers of bacteria (105 /ml - 106 /ml) in order to identify transcriptional fusions induced during the experiment. For the STM approach we used a large collection of Tn5 tagged mutants (Pobigaylo et al. 2006) using the same experimental design. To determine and compare the proportion mutants between the input (inoculum) and the output (root associated rhizobia) conditions we used microarrays and Illumina HiSeq sequencing platform. Both approaches were able to identify genes (pyrE, metA, SM2011_c04258) that might be of relevance for the early root colonization. Of the identified genes, only few (pyrE, metA) have been previously described as involved in nodule competition (Pobigaylo et al.).