Scientists at the Carnegie Institution have found that a plant steroid is behind stimulation of two genes - one suppressing the other for ensuring that leaves grow normally in rice and the experimental plant Arabidopsis thaliana, which is a relative of mustard - to battle against each other.

The results appeared in the December 15, 2009, issue of The Plant Cell and are believed to provide implications for understanding as to how manipulations can be observed in context to crop growth and yield.

From Sciencedaily.com:

Co-author Zhi-Yong Wang at Carnegie’s Department of Plant Biology explained the work: “We knew that the steroid is very important for activating genes that control cell growth in Arabidopsis as well as in rice. One of the most sensitive responses to the steroid is leaf bending in rice, caused by expansion of the upper cells at the joint between leaf blade and leaf sheath. We wanted to determine how the steroid functioned in rice. We found that the steroid affects two genes encoding (or producing) proteins that turn other genes on or off; they are called transcription factors. In rice, when a gene called Increased Leaf Inclination1 (ILI1) is turned on, it causes leaf bending. Interestingly, we found that the ILI1 protein also binds to another transcription factor, called IBH1, and inhibits its function. When there is too much ILI1 protein, the leaves bend excessively making the plant shaggy. When IBH1 level is high, cell growth is stopped at the joint and the rice is very erect, taking up less space. In normal rice plants the balance between ILI1 and IBH1 keeps growth in check.”

This pair of genes provides a unique tool to control the leaf angle, which is important for crop yield because erect leaves improve light capture and allows rice plants to be planted at higher density for a higher yield per hectare.

The list of study colleagues were from the following institutions: Institute of Botany, Chinese Academy of Sciences; Chinese Academy of Agricultural Sciences; Department of Plant Biology, Carnegie Institution; Yonsei University, Korea; RIKEN Advanced Science Institute, Japan.