Scientists have revealed how the plant hormone auxin enables roots to bend downward toward gravity — a process known as gravitropism — even when roots encounter obstacles in the soil.
Researchers from the University of Nottingham’s School of Biosciences and Shanghai Jiao Tong University (SJTU) discovered that auxin activates a specific gene that strengthens cell walls on the lower side of the root. This reinforcement limits growth below the root while allowing cells above to expand, causing the root to bend downward.
Gravitropism shapes root angles and the overall root system by creating differences in cell expansion between the upper and lower sides of roots. The study was published in Science Advances.
“Until now it was unclear how auxin inhibits cell expansion on the lower side of roots,” Dr. Rahul Bhosale, Associate Professor in the School of Biosciences who co-led the study, said.
“Our research resolves this longstanding question by showing that auxin promotes cell wall biosynthesis, strengthening the walls to block growth on the lower side. This dual mechanism explains auxin’s seemingly opposite roles in promoting and inhibiting cell elongation.”
This research builds on the team’s earlier work showing that the hormone abscisic acid (ABA), which helps plants respond to drought, alters root growth angles by influencing auxin levels under water stress. Together, these findings provide a clearer understanding of how roots sense their environment and adjust their growth direction, according to a press release.
“We already knew that auxin is important for root gravitropism, but for a long time, we did not know what acts downstream of auxin,” Dr Bhosale added. “That is what we have uncovered in this new research which is important for fundamental understanding of how the root system works. Understanding the role of hormones in this much detail opens up possibilities for engineering crops that are stress resistant and can overcome obstacles in the soil.”
