Constitutive Expression of ACC Deaminase in Mesorhizobium loti Promotes Nodulation

VALERIA CONFORTE; MARIELA ECHEVERRÍA; RODOLFO UGALDE; ANA MENÉNDEZ

Mar del Plata

Congreso; XLIII Reunión Anual SAIB; 2007

SAIB

Ethylene inhibits the establishment of symbiosis between rhizobia and legumes. Several rhizobia species express the enzyme ACC deaminase, which degrades ACC (precursor of ethylene) leading to the reduction of the amount of ethylene evolved by the plant. M. loti has a gene that encodes ACC deaminase but it is under the activity of a NifA-rpoN-dependent promoter thus, it is only expressed in the bacteroid form, inside nodule. We wanted to know if the presence of ACC deaminase activity in the first steps of the -Lotus interaction could promote the efficiency of the nodulation process. M. loti ACC deaminase structural gene (acdS) was introduced into M. loti MAFF303099 and Ayac 1BII in a plasmid vector, replicative in rhizobia, upon the constitutive promoter activity of Plac. The resulting strains show high ACC deaminase activity in the free-living cells. Nodulation assays were carried out with the wild-type as well as with the constitutive ACC deaminase-producing strains. Data showed that the recombinant strains induced more nodules (2-2,8 /plant) than the wild-type ones (1-1,5 /plant). This result indicates that there could be a good possibility to increase the nodulation efficiency in field by the use as inocula these genetically engineering strains.