Abstract
We have isolated a number of shoot gravitropism (sgr) mutants of Arabidopsis to elucidate the molecular mechanism ofshoot gravitropism. We have previously shown that the endodermal cells, which contain sedimented amyloplasts, are essential for shoot gravitropism. sgr6 recessive mutants exhibited reduced gravitropic response in the inflorescence stems. Interestingly, sgr6-1 had sedimented amyloplasts and exhibited normal phototropism. We identified the SGR6 gene, which encodes a protein with 1703 amino acids by a map-based cloning. Well-conserved functional domains were not found in SGR6. Endodermis-specific expression of the SGR6 could complement the abnormal shoot gravitropism of sgr6-1. These results suggest that SGR6, which is a novel protein with unknown function, is involved in the gravi-perception and the signal transduction process which take place in the encodermal cells.
