XVI International Botanical Congess

Mutants in ARG1 (altered response to gravity) display defects in hypocotyl and root gravitropism, albeit normal phototropism. They accumulate starch normally in their statocytes, and have a wild type response to plant hormones and auxin-transport inhibitors. These observations suggest that ARG1 is not involved in the sensing, signaltransmission, or response phases of gravitropism. ARG1 may be part of the signal transduction machinery that converts gravity signals tophysiological signals, leading eventually to the curvature response ofthe organs. ARG1 has been cloned by Sedbrook et al. (1999. PNAS: 96, 1140). It encodes a DnaJ-like protein with a J domain at its N-terminus, a transmembrane helix, and a coiled coil domain with sequence similarity to coiled coil portions of cytoskeleton-interacting proteins. GFP fusions of ARG1 have been constructed and transformed into plants to study the protein distribution.