The A rabidopsis GIBBERELLIN METHYL TRANSFERASE 1 suppresses gibberellin activity, reduces whole‐plant transpiration and promotes drought tolerance in transgenic tomato

• Published in: Plant, cell and environment Vol. 37; no. 1; pp. 113 - 123
• Main Authors: NIR, IDO, MOSHELION, MENACHEM, WEISS, DAVID
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12135

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 ( S olanum 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 A rabidopsis 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. Previous studies have shown that reduced gibberellin ( GA ) activity promotes plant tolerance to osmotic stresses, but the underlying mechanism is not clear yet. In this study we expressed the recently discovered GIBBERELLIN METHYL TRANSFERASE 1 ( GAMT1 ) gene in tomato plants to reduce the levels of active GAs . The transgenic plants exhibited typical GA ‐deficiency phenotypes and increased tolerance to drought stress. The transgenic leaves had smaller stomata with reduced pores, leading to reduced stomatal conductance and whole‐plant transpiration.