Plants rapidly colonize surrounding environments by directing and coordinating the growth of root system. Polar, cell-to cell transport of phytohormone auxin controls the root organ bending in response to gravity. However, it remains unknown what mechanisms counterbalance these auxin-mediated organ bending, particularly in the environments where the water becomes easily accessible near the surface. Using genome-wide study combined with root growth kinetics and computer modeling we show that major hormone cytokinin acts as anti-gravitropic queue that reduces the bending of lateral organs and thereby controls the radial expansion of plant root system.
Nordic plants with flat root systems carries a specific mutation in the of Cytokinin Oxidase 2 (CKX2) that aborts enzymatic activity of CKX2 towards cytokinin degradation. Furthermore, cytokinin signaling remains strongly asymmetric and counteracts auxin mediated responses by locally controlling cell growth.
Our study pinpoints how enemies in phytohormone world controls each other queues to fine tune plant root architecture and maximize efficiency towards water consumption.