Modulation of ethylene biosynthesis by plant growth promoting rhizobacteria and its importance for arbuscular mycorrhiza development

Abstract

The molecular mechanisms controlling the different stages of arbuscular mycorrhiza (AM) development are beginning to be elucidated. Studies with several plant species point to the important regulatory role of phytohormones on the development of AM. Besides the correlative data, genetic and transgenic approaches have shown evidence of ethylene signaling during mycorrhizal colonization. In general, high concentrations of ethylene in the roots are correlated with inhibition of AM development. However, little is known on the mechanisms modulating ethylene biosynthesis during the development and functioning of AM. In roots, part of the immediate ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), produced under biotic and abiotic stresses, may be secreted and metabolized by rhizosphere microorganisms, mostly bacteria. Rhizobacteria with the ability to degrade ACC may induce a reduction in ethylene concentration in roots and enhance plant tolerance to stresses, as well as modulate interactions with symbiotic microorganisms, including arbuscular mycorrhizal fungi (AMF). Thus, ACC-degrading rhizobacteria might be used as new biofertilizers for promoting plant growth and stimulating AM development. Since this strategy was not fully explored so far, the aims of this proposal are to determining whether the ACC-deaminase producing rhizobacteria may stimulate AM development through the reduction of ethylene concentration in the roots, and whether such bacteria may be used to stimulate mycorrhizal colonization by native AMF and plant growth. The University of California-Riverside has a valuable collection of ACC-degrading rhizobacterial isolates, which will be used for the proposed experiments. (AU)