Active cell division takes place in the tip of a plant's root, where different zones work together to expand into new depths of the soil. Optimal root growth rate is important for plant survival and maximizing resource allocation to important plant parts. This is why root-expansion mechanisms are of great interest to scientists and to those interested in improving agricultural yields.

One of the major driving factors of root tip growth discovered by Juthamas Chaiwanon and Zhiyong Wang from Carnegie Institution for Science is the class of steroid hormones called brassinosteroids, which they found to act on a concentration gradient to regulate root growth patterns. In many parts of a plant, brassinosteroids function cooperatively with the plant hormone auxin. But Chaiwanon and Wang's results show, surprisingly, that in root tip growth, brassinosteroids and auxin had opposite effects on root cell elongation, and the balance between their actions regulated a root's growth rate.

The team identified more than 2,000 genes that are regulated by both brassinosteroid and auxin, and about 70 percent of these co-regulated genes responded to brassinosteroids and auxin in opposite directions—being turned on by one and off by the other or vise versa.

For more information about this research, read the news article at the Carnegie website.

Figure: Carnegie Institution for Science