Control of adventitious root formation: insights into synergistic and antagonistic hormonal interactions.

Plants have evolved sophisticated root systems that help them to cope with harsh environmental conditions. They are typically composed of a primary root and lateral roots (LRs), but may also include adventitious roots (ARs). Unlike LRs, ARs may be initiated not only from pericycle cells, but from various cell types and tissues depending on the species. Phytohormones, together with many other internal and external stimuli, coordinate and guide every step of AR formation from the first event of cell reprogramming until emergence and outgrowth. In this review, we summarize recent advances in the molecular mechanisms controlling AR formation and highlight the main hormonal cross talk involved in its regulation under different conditions and in different model systems.