The EU-funded SIDEWAYS (Final size determination through spatio-temporal regulation of phytohormone signaling pathways) project has investigated brassinosteroids (BRs) to work out how their chemical signals can control final size. Using the model plant Arabidopsis, the researchers first showed that BRs are required to maintain normal cell cycle activity and cell expansion in the root meristem. Highly significant, the researchers showed in several instances that the BR signal controls growth in an opposing manner, depending of the site of hormone perception. This strategy is used to control different set of genes that balance the extent of growth. For example, auxin genes, activated by epidermal BR signals are necessary for induction of cell division. Conversely, when the BR signals emanate from the stele in the central part of the root or stem, accompanied by gene repression, the epidermal effect is restrained. Moreover, the scientists discovered very complex control networks involving BR sensitivity in the root that is responsible for fine-tuning growth. Root cells that form hair cells are coordinated with neighbouring cells that do not form hairs – expression of receptor BRI1 in hair cells promotes cell elongation in all tissues whereas high levels in non-hair cells inhibit cell elongation. This indicates that signalling between hair and non-hair cells brings about changes in growth rate and is a result of genetic and mechanical factors. BR genetic modification has already been used in the agricultural sector to increase crop yield. The control processes discovered by the SIDEWAYS project will enable geneticists to improve various crop traits without impinging on other characteristics. Project achievements have also resulted in attendance at international meetings and valuable research collaborations in the field of control of plant growth.
Growth, plant, BR, chemical signals, crop yield