Chapter 14 - Beneficial plant-microbe interactions

Abstract

The chapter presents general ideas concerning the ecological and practical prospects for the application of beneficial plant–microbe interactions. In order to use them in constructing novel sustainable agro-systems, cooperation of specialists from different fields of microbial and plant research is required. The most beneficial plant–microbe system is the nitrogen-fixing symbiosis formed by leguminous plants and nodule bacteria (rhizobia). Legume genes control the nodule development. The nodule number in legumes is regulated by numerous factors including the genotype of the bacterial partner and environmental factors (temperature, drought, salinity, N and P nutrition, pollution). From the rhizobial side, the correlation between specificity and taxonomy is even more questionable than from the plant side. Application of the traditional methods was limited by the lack of expression of many symbiotic genes in the free-living cells and this limitation was avoided by using transposons. The section on specificity and signaling discusses host-specific decorations as well as how the host specificity of nodulation is provided by the signal exchange between legume plants and nodule bacteria. It also lists the impacts of the host-defense reactions. The principal genetic strategy for the formation of the integrated biochemical system in a nodule is represented by the strictly coordinated expression of symbiotic genes in the interacting plant and rhizobial cells. A table in the chapter compares two types of N2-fixing plant–microbe symbioses. The chapter also describes mycorrhizae; they represent the most broadly distributed strategy of plant–microbe symbiosis. One of the basic strategies in plant–microbe interactions is to protect the plants against their natural enemies, pathogenic microbes, pests, and herbivores, which is also referred to as defensive symbiosis. The section on ecological and agricultural impacts of beneficial plant–microbe interactions discusses that the role of beneficial microbes in plant adaptability is to improve their nutrition.