Hypocotyls of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) do not elongate in response to exogenous auxin, but can respond to gravity. This appears paradoxical in light of the Cholodny-Went hypothesis, which states that shoot gravicurvature results from asymmetric stimulation of elongation by auxin. While light-grown dgt seedlings can achieve correct gravitropic reorientation, the response is slow compared to wild-type seedlings. The sensitivity of dgt seedlings to inhibition of gravicurvature by immersion in auxin or auxin-transport inhibitors is similar to that of wild-type plants, indicating that both an auxin gradient and auxin transport are required for the gravitropic response and that auxin uptake, efflux, and at least one auxin receptor are functional in dgt. Furthermore, dgt gravicurvature is the result of asymmetrically increased elongation as would be expected for an auxin-mediated response. Our results suggest differences between elongation in response to exogenous auxin (absent in dgt) and elongation in response to gravistimulation (present but attenuated in dgt) and confirm the presence of two phases during the gravitropic response, both of which are dependent on functional auxin transport.

The diageotropica (dgt) mutation has been proposed to affect either auxin perception or responsiveness in tomato plants. It has previously been demonstrated that the expression of one member of the Aux/IAA family of auxin-regulated genes is reduced in dgt plants. Here, we report the cloning of ten new members of the tomato Aux/IAA family by PCR amplification based on conserved protein domains. All of the gene family members except one (LelAA7) are expressed in etiolated tomato seedlings, although they demonstrate tissue specificity (e.g. increased expression in hypocotyls vs. roots) within the seedling. The wild-type auxin-response characteristics of the expression of these tomato LelAA genes are similar to those previously described for Aux/IAA family members in Arabidopsis. In dgt seedlings, auxin stimulation of gene expression was reduced in only a subset of LelAA genes (LelAA5, 8, 10, and 11), with the greatest reduction associated with those genes with the strongest wild-type response to auxin. The remaining LelAA genes tested exhibited essentially the same induction levels in response to the hormone in both dgt and wild-type hypocotyls. These results confirm that dgt plants can perceive auxin and suggest that a specific step in early auxin signal transduction is disrupted by the dgt mutation.

Roots of the tomato (Lycopersicon esculentum, Mill.) mutant (diageotropica (dgt) exhibit an altered phenotype. These roots are agravitropic and lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots are less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a reduction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated naphthylphthalamic acid ([3H]NPA), to root microsomal membranes, NPA-sensitive IAA uptake by root segments, and uptake of [3H]NPA into root segments are all similar in mutant and wild-type roots. We speculate that the reduced sensitivity of dgt root growth to auxin-transport inhibitors and ethylene is an indirect result of the reduction in sensitivity to auxin in this single gene, recessive mutant. We conclude that dgt roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin perception or action.

Tomato plants homozygous for the diageotropica (dgt) mutation exhibit morphological and physiological abnormalities which suggest that they are unable to respond to the plant growth hormone auxin (indole-3-acetic acid). The photoaffinity auxin analog [3H]5N3-IAA specifically labels a polypeptide doublet of 40 and 42 kilodaltons in membrane preparations from stems of the parental variety, VFN8, but not from stems of plants containing the dgt mutation. In roots of the mutant plants, however, labeling is indistinguishable from that in VFN8. These data suggest that the two polypeptides are part of a physiologically important auxin receptor system, which is altered in a tissue-specific manner in the mutant.

The vegetative phenotype of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) includes reduced gravitropic response, shortened internodes, lack of lateral roots, and retarded vascular development. Here, we report that early fruit development is also dramatically altered by the single-gene dgt lesion. Fruit weight, fruit set, and numbers of locules and seeds are reduced in dgt. In addition, time to flowering and time from anthesis to the onset of fruit ripening are increased by the dgt lesion, whereas ripening is normal. The dgt mutation appears to affect only the early stages of fruit development, irrespective of allele or genetic background. Expression of members of the LeACS (1-aminocyclopropane-1-carboxylic acid synthase, a key regulatory enzyme of ethylene biosynthesis) and LeIAA (Aux/IAA, auxin-responsive) gene families were quantified via real-time reverse transcriptase-polymerase chain reaction in both dgt and wild-type fruits, providing the first analysis of Aux/IAA gene expression in fruit. The dgt lesion affects the expression of only certain members of both the LeACS and LeIAA multigene families. Different subsets of LeIAA gene family members are affected by the dgt mutation in fruits and hypocotyls, indicating that the DGT gene product functions in a developmentally specific manner. The differential expression of subsets of LeIAA and LeACS gene family members as well as the alterations in dgt fruit morphology and growth suggest that the early stages of fruit development in tomato are regulated, at least in part, by auxin- and ethylene-mediated gene expression.

The diageotropica ( dgt) mutant of tomato ( Lycopersicon esculentum Mill.) is known to lack a number of typical auxin responses. Here we show that rapid auxin-induced growth of seedling hypocotyls is completely abolished by the mutation over the full range of auxin concentrations tested, and also in early phases of the time course. Protoplasts isolated from wild-type hypocotyls respond to auxin by a rapid increase in cell volume, which we measured by image analysis at a high temporal resolution. A similar swelling could be triggered by antibodies directed against a part of the putative auxin-binding domain (box-a) of the auxin-binding protein 1 (ABP1). Induction of swelling both by auxin and by the antibody was not observed in the protoplasts isolated from the dgt mutant. However, dgt protoplasts are able to respond to the stimulator of the H(+)-ATPase, fusicoccin, with normal swelling. We propose that dgt is a signal-transduction mutation interfering with an auxin-signalling pathway that uses ABP1 as a receptor.

The single gene, auxin-resistant diageotropica (dgt) mutant of tomato displays a pleiotropic auxin-related phenotype that includes a slow gravitropic response, lack of lateral roots, reduced apical dominance, altered vascular development, and reduced fruit growth. Some auxin responses are unaltered in dgt plants, however, and the levels, metabolism, and transport of auxin appear normal, indicating that the Dgt gene encodes a component of a specific auxin signaling pathway. By combining map-based cloning with comparative microsynteny, we determined that the Dgt gene encodes a cyclophilin (CYP) (LeCYP1; gi:170439) that has not previously been identified as a component of auxin signaling and plant development. Each of the three known dgt alleles contains a unique mutation in the coding sequence of LeCyp1. Alleles dgt(1-1)and dgt(1-2) contain single nucleotide point mutations that generate an amino acid change (G137R) and a stop codon (W128stop), respectively, while dgt(dp) has an amino acid change (W128CDelta129-133) preceding a 15 bp deletion. Complementation of dgt plants with the wild-type LeCyp1 gene restored the wild-type phenotype. Each dgt mutation reduced or nullified the peptidyl-prolyl isomerase activity of the GST-LeCYP1 fusion proteins in vitro. RT-PCR and immunoblot analyses indicated that the dgt mutations do not affect the expression of LeCyp1 mRNA, but the accumulation of LeCYP1 protein is greatly reduced for all three mutant alleles. The CYP inhibitor, cyclosporin A, partially mimics the effects of the dgt mutation in inhibiting auxin-induced adventitious root initiation in tomato hypocotyl sections and reducing the auxin-induced expression of the early auxin response genes, LeIAA10 and 11. These observations confirm that the PPIase activity of the tomato CYP, LeCYP1, encoded by the Dgt gene is important for specific aspects of auxin regulation of plant growth, development, and environmental responses.

The sensitivity of excised hypocotyl segments to indoleacetic acid (IAA) in two assays, ethylene production and elongation, was determined in the ethylene-requiring tomato (Lycopersicon esculentum Mill.) mutant, diageotropica (dgt), and its isogenic parent, cv VFN8. Endogenous (uninduced) ethylene synthesis rates were slightly lower in dgt hypocotyls than in VFN8 hypocotyls. Ethylene production was essentially unaffected by IAA in dgt, but was stimulated up to 10-fold by 10 micromolar IAA in VFN8. Elongation of dgt hypocotyls was also insensitive to concentrations of IAA as high as 100 micromolar, as compared to significant elongation of VFN8 hypocotyls in response to 0.1 micromolar IAA. A range of IAA analogs active in VFN8 was also ineffective in stimulating elongation of dgt hypocotyls, suggesting that the differences were not due to rapid metabolism of IAA by dgt tissues. Auxin-induced elongation of VFN8 hypocotyls was unaffected by 2,3,5-triiodobenzoic acid and naphthylphthalamic acid, indicating that polar auxin transport was not a factor in these experiments. Exogenous and auxin-induced ethylene had no effect on the elongation respone of either genotype, nor did exogenous ethylene restore the sensitivity of dgt hypocotyls to IAA. Despite their apparent insensitivity to auxin, dgt hypocotyls elongated dramatically and synthesized ethylene rapidly in response to 1.2 micromolar fusicoccin. These results suggest that the primary effect of the dgt mutation is to reduce the sensitivity of the tissue to auxin. As altered regulation of ethylene synthesis is only one symptom of this fundamental deficiency, dgt should more properly be considered to be the auxin-insensitive tomato mutant.

We analyzed the impact of ethylene and auxin disturbances on callus, shoots and Agrobacterium rhizogenes-induced hairy root formation in tomato (Solanum lycopersicum L.). The auxin low-sensitivity dgt mutation showed little hairy root initiation, whereas the ethylene low-sensitivity Nr mutation did not differ from the control Micro-Tom cultivar. Micro-Tom and dgt hairy roots containing auxin sensitivity/biosynthesis rol and aux genes formed prominent callus onto media supplemented with cytokinin. Under the same conditions, Nr hairy roots did not form callus. Double mutants combining Rg1, a mutation conferring elevated shoot formation capacity, with either dgt or Nr produced explants that formed shoots with little callus proliferation. The presence of rol + aux genes in Rg1 hairy roots prevented shoot formation. Taken together, the results suggest that although ethylene does not affect hairy root induction, as auxin does, it may be necessary for auxin-induced callus formation in tomato. Moreover, excess auxin prevents shoot formation in Rg1.

The community resource presented here is a useful toolkit for plant research, particularly for future studies in plant development, which will require the simultaneous observation of the effect of various hormones, signaling pathways and crosstalk.

The SELF PRUNING (SP) gene is a key regulator of growth habit in tomato (Solanum lycopersicum). It is an ortholog of TERMINAL FLOWER1, a phosphatidylethanolamine-binding protein with antiflorigenic activity in Arabidopsis (Arabidopsis thaliana). A spontaneous loss-of-function mutation (sp) has been bred into several industrial tomato cultivars, as it produces a suite of pleiotropic effects that are favorable for mechanical harvesting, including determinate growth habit, short plant stature, and simultaneous fruit ripening. However, the physiological basis for these phenotypic differences has not been thoroughly explained. Here, we show that the sp mutation alters polar auxin transport as well as auxin responses, such as gravitropic curvature and elongation of excised hypocotyl segments. We also demonstrate that free auxin levels and auxin-regulated gene expression patterns are altered in sp mutants. Furthermore, diageotropica, a mutation in a gene encoding a cyclophilin A protein, appears to confer epistatic effects with sp Our results indicate that SP affects the tomato growth habit at least in part by influencing auxin transport and responsiveness. These findings suggest potential novel targets that could be manipulated for controlling plant growth habit and improving productivity.

Auxin modulates a range of plant developmental processes including embryogenesis, organogenesis, and shoot and root development. Recent studies have shown that plant hormones also strongly influence metabolic networks, which results in altered growth phenotypes. Modulating auxin signalling pathways may therefore provide an opportunity to alter crop performance. Here, we performed a detailed physiological and metabolic characterization of tomato (Solanum lycopersicum) mutants with either increased (entire) or reduced (diageotropica-dgt) auxin signalling to investigate the consequences of altered auxin signalling on photosynthesis, water use, and primary metabolism. We show that reduced auxin sensitivity in dgt led to anatomical and physiological modifications, including altered stomatal distribution along the leaf blade and reduced stomatal conductance, resulting in clear reductions in both photosynthesis and water loss in detached leaves. By contrast, plants with higher auxin sensitivity (entire) increased the photosynthetic capacity, as deduced by higher Vcmax and Jmax coupled with reduced stomatal limitation. Remarkably, our results demonstrate that auxin-sensitive mutants (dgt) are characterized by impairments in the usage of starch that led to lower growth, most likely associated with decreased respiration. Collectively, our findings suggest that mutations in different components of the auxin signalling pathway specifically modulate photosynthetic and respiratory processes.