Plants are capable of orienting their root growth towards gravity in a process termed gravitropism, which is necessary for roots to grow into soil, for water and nutrient acquisition and to anchor plants. Here we show that root gravitropism depends on the novel protein, NEGATIVE GRAVITROPIC RESPONSE OF ROOTS (NGR). In both Medicago truncatula and Arabidopsis thaliana, loss of NGR reverses the direction of root gravitropism, resulting in roots growing upward.
We thank A. Laxmi and Y. Tang for the microarray experiments, G. Li for Medicago crossing, E. Blancaflor for microscopy, X. Cheng and J. Wen for reverse genetics screen. We thank K. Mysore for providing Medicago Tnt1 lines and ABRC for Arabidopsis T-DNA lines. Funding for Medicago genetic resources was provided by National Science Foundation (IOS-1127155) to R. C. Funding of this work was provided by The Samuel Roberts Noble Foundation, Inc.