Plant shoot to root communication has been established previously, but little has been understood about the molecular basis of the long-distance shoot-root coordination. A new study conducted by researchers from the University of Oxford and the Chinese Academy of Sciences in China shows that communication is achieved through a moving agent from shoot to root. The agent is a protein known as HY5, a transcription factor that activates, or "switches on" genes.

HY5 was already known to control rates of photosynthesis (CO2 capture) in the shoot, but the study shows that HY5 acts as an agent of communication between shoot and root by moving through the phloem vessels of the plant. HY5 travels from shoot to root, and when it reaches the root it activates a number of genes in root cells, including genes that encode the nitrate transporters that extract nitrate from the soil. This activation is also dependent upon sugars that also travel through the phloem from shoot to root. Thus, movement of HY5 and sugars from shoot to root increases nitrate uptake by the root. Plant breeders can now target HY5 to increase its activity in the roots of shaded crop plants, to improve nitrate uptake from the soil.

For more information, read the article at the University of Oxford Science Blog.