The constitutive expression of ACC deaminase in Mesorhizobium loti promotes nodulation on Lotus glaber under stress conditions.

VALERIA CONFORTE; MARIELA ECHEVERRÍA; RODOLFO UGALDE; ANA MENÉNDEZ; VIVIANA LEPEK

Chascomús

Taller; IV Interdisciplinary Workshop of Lotus; 2008

The biosynthesis of phytohormone ethylene is accelerated in association with environmental and biological stresses. Ethylene inhibits the synthesis between rhizobia and legumes. Several rhizobia species have developed mechanisms to reduce the ethylene levels in their host legume. Meshorhizobium loti has the acdS gene which codifies for an enzyme with ACC deaminase activity. This enzyme converts the ethylene synthesis precursor, 1-aminocyclopropane-1-carboxylate (ACC), into α-ketobutyrate and ammonia. This bacterium expresses this gene only in the bacteroid state, inside the nodules. Our hypothesis is that the constitutive expression of this gene in the vegetative state will promote higher nodulation efficiency in the stress conditions to which bacteria are subjected in the soil. To test this, we integrated in the M. loti MAFF303099 chromosome an acdS copy under the activity of a constitutive promoter and we analyzed its nodulation efficiency under different stress conditions. M. loti expressing acdS constitutively resulted more competitive than the wild type strain on Lotus glaber that had been grown for 52 days without a nitrogen source before inoculation. On the other hand, the transconjugant strain showed a tendency to induce higher number of nodules than the wild type strain when inoculation was made on plants subjected to stress by illumination.