Measurements of gravitropism in shoots (A; Ler n = 15, grv2-1 n = 12, Col n = 8, grv2-2 n = 14, grv2-3 n = 12, grv2-4 n = 12), hypocotyls (B; Ler, n = 15–37; grv2-1, n = 10–29; Col, n = 19; grv2-4, n = 21), and roots (C; Ler, n = 148; grv2-1, n = 132; Col, n = 19; grv2-2, n = 16; grv2-3, n = 15; grv2-4, n = 21) in grv2 mutants and wild types. Error bars represent the se of the mean.

Measurements of phototropism in shoots (A; Ler, n = 9; grv2-1, n = 10; Col, n = 7; grv2-2, n = 6; grv2-3, n = 6; grv2-4, n = 6) and hypocotyls (B; Ler, n = 27–34; grv2-1, n = 23–34; Col, n = 11–23; grv2-4, n = 24–32) in grv2 mutants and wild types. Error bars represent the se of the mean.

Structure of the GRV2 locus. A, The region of chromosome II containing the GRV2 gene was spanned by bacterial artificial chromosomes F12C20 and T20P8 (www.arabidopsis.org). A cosmid contig spanning the GRV2 gene is shown as overlapping lines beneath The Arabidopsis Information Resource annotation of the region. The three genes in the complementing cosmid, pRAM011, are At2g26870 (a), At2g26880 (b), and At2g26890 (c). B, The intron-exon structure of the GRV2 gene (At2g26890) is shown as lines and boxes, respectively. The locations of various mutations are indicated by lines and arrowheads. grv2-1 has an 85-residue truncation, grv2-4 has a frame shift resulting in a stop codon in exon 11, and GT1669 and SALK 067162 are T-DNA insertions. A schematic drawing of the GRV2 protein is shown below the transcript schematic. White boxes represent IWN repeat domains, and the black circle represents the J domain. The expressed sequence tag, RZL04ho7, and the reverse transcription-PCR products that were sequenced to determine the intron-exon structure (α, β, γ, δ, ɛ, ξ, η, θ, ι) are shown beneath the protein structure.

Expression pattern of GRV2 promoter GUS fusion in wild-type seedling and flower (inset).

Growth habit and gravitropic response of Ler wild type and the grv2-1 mutant. A and C, Wild type; B and D, grv2-1 mutant. The pots in C and D were placed in a horizontal orientation for 3 h in darkness before the photograph was taken.

Gravitropic response of wild type (A) and the grv2-1 mutant (B). Three-day-old seedlings, germinated on vertically oriented agar-solidified medium in darkness, were turned 90 degrees and photographed after 12 h.

Microscopic image of thin sections of primary inflorescence shoots (3–4 cm below the apex) from wild type (A and C) and the grv2-1 mutant (B and D). The stems were fixed with the gravity direction maintained. The arrows point to amyloplasts. The bars indicate 20 μm (A and B) and 1 μm (C and D).

RNAse protection assays of GRV2 mRNA from various tissues of wild type. The four fragments correspond to GRV2 DNA (484 bp), GRV2 RNA (387 bp), UBC1 DNA (245 bp), and UBC1 RNA (150 bp) Lanes: R, roots; RL, rosette leaves; St, stems; CL, cauline leaves; F, flowers; Si, siliques.