Poster: Hormones

Abs # 606: The Diageotropica Gene of Tomato Encodes a Novel Player, a Cyclophilin, in Auxin Signaling.

Presenter:	Oh, KwangChul , ohk@science.oregonstate.edu
Authors	Oh, KwangChul  (A)   Ivanchenko, Maria G (A)   White, Tj  (A)   Lomax, Terri L (A)
Affiliations:	(A): Oregon State University

The single gene, auxin-resistant diageotropica (dgt) mutant of tomato displays a pleiotropic phenotype that includes a slow gravitropic response, lack of lateral roots, reduced apical dominance, altered vascular development, and reduced fruit growth. Interestingly, the dgt mutation appears to affect the expression of only a subset of auxin-regulated genes. We hypothesize that the Dgt gene encodes a component in the auxin signal transduction pathway since dgt plants do not exhibit altered levels, metabolism, or transport of auxin. By combining map-based cloning with a comparative microsynteny approach, we determined that the Dgt gene encodes a cyclophilin (LeCYP1), a previously unidentified component of auxin signaling. Each known dgt allele contains a unique mutation in the coding sequence of LeCyp1. Single nucleotide point mutations generate an amino acid change (G₁₃₇R) and stop codon (W₁₂₈stop) in dgt^1-1 and dgt^1-2, respectively, and dgtdp has an amino acid change (W₁₂₈C∆129-133) preceding a 15 bp deletion. Complementation of dgt mutant plants with LeCyp1 restored the wild-type phenotype. Allelic mutations reduced or nullified PPIase activity of glutathione S-transferase (GST)–CYP fusion proteins in vitro. RT-PCR and immunoblot analyses indicate that the expression of LeCyp1 mRNA does not appear to be affected by the dgt mutation but the accumulation of LeCYP1 proteins is greatly reduced for all three alleles. The cyclophilin inhibitor, cyclosporin A, inhibits auxin-induced adventitious root initiation in hypocotyl sections and reduces the auxin-induced expression of the early auxin response genes, LeIAA10 and 11, providing further support that the tomato cyclophilin encoded by the Dgt gene is a new and novel player in auxin signal transduction pathways.