title: The Arabidopsis gibberellin methyl transferase 1 suppresses gibberellin activity, reduces whole-plant transpiration and promotes drought tolerance in transgenic tomato.
abstract: Previous studies have shown that reduced gibberellin (GA) level or signal promotes plant tolerance to environmental stresses, including drought, but the underlying mechanism is not yet clear. Here we studied the effects of reduced levels of active GAs on tomato (Solanum lycopersicum) plant tolerance to drought as well as the mechanism responsible for these effects. To reduce the levels of active GAs, we generated transgenic tomato overexpressing the Arabidopsis thaliana GA METHYL TRANSFERASE 1 (AtGAMT1) gene. AtGAMT1 encodes an enzyme that catalyses the methylation of active GAs to generate inactive GA methyl esters. Tomato plants overexpressing AtGAMT1 exhibited typical GA-deficiency phenotypes and increased tolerance to drought stress. GA application to the transgenic plants restored normal growth and sensitivity to drought. The transgenic plants maintained high leaf water status under drought conditions, because of reduced whole-plant transpiration. The reduced transpiration can be attributed to reduced stomatal conductance. GAMT1 overexpression inhibited the expansion of leaf-epidermal cells, leading to the formation of smaller stomata with reduced stomatal pores. It is possible that under drought conditions, plants with reduced GA activity and therefore, reduced transpiration, will suffer less from leaf desiccation, thereby maintaining higher capabilities and recovery rates.
authors.affiliation: Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel.
authors.forename: Ido
authors.initials: I
authors.lastname: Nir
authors.forename: Menachem
authors.initials: M
authors.lastname: Moshelion
authors.forename: David
authors.initials: D
authors.lastname: Weiss
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D055864:Droughts; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D054046:Plant Stomata / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D030821:Plants, Genetically Modified; D036226:Seedlings / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D013312:Stress, Physiological
chemical_list: D029681:Arabidopsis Proteins; D005875:Gibberellins; D010937:Plant Growth Regulators; C519869:GAMT1 protein, Arabidopsis; D008780:Methyltransferases
keywords: GAMT1; drought stress; stomata; transpiration