Beneficial Microbes Affect Endogenous Mechanisms Controlling Root Development

Interaction between plant roots and the beneficial bacteria within their rhizosphere shapes the bacteria community composition, and enhances plant growth and plant pathogen defense. Plant growth-promoting rhizobacteria (PGPR) affect cell division and differentiation leading to changes in root system architecture, which contributes to enhanced shoot growth. These modifications are established by changing plant endogenous signaling pathways. While several PGPR can produce phytohormones, many effects on plant developmental pathways are exerted by other molecules. Several fungi have the same effects on root system architecture as PGPR, indicating that growth-promoting mechanisms might be conserved across kingdoms. Plants have incredible developmental plasticity, enabling them to respond to a wide range of environmental conditions. Among these conditions is the presence of plant growth-promoting rhizobacteria (PGPR) in the soil. Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development. These effects lead to dramatic changes in root system architecture that significantly impact aboveground plant growth. Thus, PGPR may promote shoot growth via their effect on root developmental programs. This review focuses on contextualizing root developmental changes elicited by PGPR in light of our understanding of plant–microbe interactions and root developmental biology. Plants have incredible developmental plasticity, enabling them to respond to a wide range of environmental conditions. Among these conditions is the presence of plant growth-promoting rhizobacteria (PGPR) in the soil. Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development. These effects lead to dramatic changes in root system architecture that significantly impact aboveground plant growth. Thus, PGPR may promote shoot growth via their effect on root developmental programs. This review focuses on contextualizing root developmental changes elicited by PGPR in light of our understanding of plant–microbe interactions and root developmental biology. phytohormone that, among other plant processes, is involved in cell division and specification in the root meristem as well as formation of lateral root primordia. a waxy cell-wall thickening in the root endodermis that restricts the flow of solutes and water into and out of the central vasculature. This barrier also restricts bacteria and fungi from entering these cells. The Casparian strip is a hallmark of differentiated endodermis. phytohormone that often functions antagonistically of auxin. In root development, cytokinin induces differentiation of cells as the move shootward. microorganisms living within plant tissue without causing harm to the plant. phytohormone involved in regulation of cell size, aging, and fruit ripening. signaling molecule produced by the plant that regulates a broad range of cellular processes from cell division and plant defense to aging. Examples include auxin, cytokinin, and ethylene. bacteria found in the rhizosphere that promote plant growth or health either directly or indirectly. a process by which bacteria measure their density and modify their behavior accordingly, i.e., to form biofilms, produce antibiotics, or coordinate virulence. the thin layer of soil around plant roots that is influenced by the root and its exudates. The rhizosphere harbors a more numerous, but less diverse, group of microorganisms than the surrounding bulk soil. the group of cells near the root tip that contains the initials, or stem cells, and quiescent cells. Together these cells supply cells that enable primary root elongation and root topology. A stem cell niche is established in the tip of lateral roots during their formation.