The gibberellin precursor GA12 acts as a long-distance growth signal in Arabidopsis.

The gibberellin (GA) phytohormones play important roles in plant growth and development, promoting seed germination, elongation growth and reproductive development(1). Over the years, substantial progress has been made in understanding the regulation of GA signalling and metabolism, which ensures appropriate levels of GAs for growth and development(2). Moreover, an additional level of regulation may reside in the transport of GAs from production sites to recipient tissues that require GAs for growth. Although there is considerable evidence suggesting the existence of short- and long-distance movement of GAs in plants(3-8), the nature and the biological properties of this transport are not yet understood. Here, we combine biochemical and conventional micrografting experiments in Arabidopsis thaliana to show that the GA precursor GA12, although biologically inactive by itself, is the major mobile GA signal over long distances. Quantitative analysis of endogenous GAs in xylem and phloem exudates further indicates that GA12 moves through the plant vascular system. Finally, we demonstrate that GA12 is functional in recipient tissues, supporting growth via the activation of the GA signalling cascade. Collectively, these results reveal the existence of long-range transport of endogenous GA12 in plants that may have implications for the control of developmental phase transitions and the adaptation to adverse environments.