Lateral Root versus Nodule: The Auxin-Cytokinin Interplay

Nodules are formed as a result of symbiosis with nitrogen-fixing bacteria on the roots of legume plants. Symbiotic nodule development shares common developmental processes with lateral roots, including cell proliferation of the pericycle and cortical cell layers leading to primordium formation, and both these organs are assumed to be evolutionarily related. The progression of their development is realized with the help of phytohormones, in particular auxin and cytokinin. Due to common evolutionary origin, the hormonal pathway and response may have similar functionality in cell fate specification during lateral root and nodule development. It is known that auxin and cytokinin both positively regulate nodule primordia development. However during lateral root development, auxin is a key positive regulator, while cytokinin suppresses lateral root development. Therefore, a comparative review of auxin and cytokinin action in the development of these two organs to elucidate how their identity is established should be of special interest. This review discusses the involvement of auxin and cytokinin in the development of symbiotic nodules and lateral roots, with a special focus on the similarity and differences of their action during lateral root and nodule developmental processes. The spatio-temporal peculiarities of auxin and cytokinin biosynthesis, transport and response during lateral root and symbiotic nodule formation are reviewed, which should help to clarify how the identity of these two root lateral organs depends on auxin-cytokinin interplay. [GRAPHICS] .

Automated summary

Nodules are formed on legume plant roots due to symbiosis with nitrogen-fixing bacteria, and their development is similar to that of lateral roots. Phytohormones auxin and cytokinin play important roles in their development. Comparing the action of auxin and cytokinin in the development of nodules and lateral roots can help to understand their identity establishment.