GSA-1/ARG1 protects root gravitropism in Arabidopsis under ammonium stress



  • Gravitropism plays a critical role in plant growth and development, plant stability and acclimation to changes in water and nutrient availability. Ammonium (NH4+) is well known to have profound effects on root growth, but its impacts on gravitropism are poorly understood.
  • To determine which genes are essential for the maintenance of root gravitropism under NH4+ stress, we isolated and identified an NH4+-sensitive mutant, gsa-1 (gravitropism sensitive to ammonium-1), in Arabidopsis thaliana, using an agar plate root reorientation assay.
  • We found that, under NH4+ stress, gsa-1 displayed increased loss of root gravitropism. Gene cloning and sequencing revealed that gsa-1 contains a G to C transversion mutation at the highly conserved 5′-GT splice position of intron 10 of ARG1 (ALTERED RESPONSE TO GRAVITY1), known to participate in the transduction of the root gravity signal. Genetic complement tests established the locus of GSA-1/ARG1 and its role in resistance to NH4+ inhibition on root gravitropism. GSA-1/ARG1 is required for normal AUX1 expression and basipetal auxin transport in root apices. In addition, PIN-FORMED2 (PIN2) is proposed as a target in the reduction of root gravitropism under NH4+ stress, a response which can be antagonized by the GSA-1/ARG1-dependent pathway.
  • These results suggest that GSA-1/ARG1 protects root gravitropism in Arabidopsis thaliana under ammonium stress.