Plant, mycorrhizal fungi, and bacterial network

Abstract

There are some kinds of beneficial symbiotic and nonsymbiotic association between different soil microbes such as arbuscular mycorrhizal (AM) fungi and plant growth-promoting rhizobacteria (PGPR) with their host plants, resulting in the establishment of a sophisticated natural network. The growth of AM fungal spores results in the production of an extensive hyphal network, which can significantly increase the uptake of nutrients and water by the host plant. In the bacterial symbiosis, like rhizobium (as PGPR), the bacteria are able to initiate some cellular structures (nodules), which are actually plant-differentiated tissues and fix the atmospheric nitrogen (N) to be used by the host plant. For the initiation of such kind of symbioses and hence the establishment of the network, signal molecules must be exchanged between the two symbionts. Signal molecules are some kind of biochemical molecules, produced by plant roots and microbes, triggering genetic activation in both symbionts. However, there are some differences differentiating microbial symbiotic association from each other. For instance, AM fungal species are able to colonize a wide range of host plants, with their signal molecules indicating their nonspecific symbiotic association, while rhizobium bacteria are able to establish symbiosis with their specific host plant, which is due to the nature of their signal molecules. It is, therefore, important to indicate the precise details regarding the signal molecules including the plant hormones, which can establish such kind of symbioses and network and the interactions between the microbes. These details can be useful for the production of more efficient inoculums and a more productive and healthy environment. The most recent advancements are presented.