Nucleotide Sequence and Spatial Expression Pattern of a Drought- and Abscisic Acid-Induced Gene of Tomato

Abstract

The nucleotide sequence of 1e16, a tomato (Lycopersicon esculentum Mill.) gene induced by drought stress and regulated by abscisic acid specifically in aerial vegetative tissue, is presented. The single open reading frame contained within the gene has the capacity to encode a polypeptide of 12.7 kilodaltons and is interrupted by a small intron. The predicted polypeptide is rich in leucine, glycine, and alanine and has an isoelectric point of 8.7. The amino terminus is hydrophobic and characteristic of signal sequences that target polypeptides for export from the cytoplasm. There is homology (47.2% identity) between the amino terminus of the LE16 polypeptide and the corresponding amino terminal domain of the maize phospholipid transfer protein. 1e16 was expressed in drought-stressed leaf, petiole, and stem tissue and to a much lower extent in the pericarp of mature green tomato fruit and developing seeds. No expression was detected in the pericarp of red fruit or in drought-stressed roots. Expression of 1e16 was also induced in leaf tissue by a variety of other abiotic stresses including polyethylene glycol-mediated water deficit, salinity, cold stress, and heat stress. None of these stresses or direct applications of abscisic acid induced the expression of 1e16 in the roots of the same plants. The unique expression characteristics of this gene indicates that novel regulatory mechanisms, in addition to endogenous abscisic acid, are involved in controlling gene expression.During a period of drought stress, a plant undergoes a number of physiological and metabolic changes together with an increase in the biosynthesis of the plant hormone ABA (38). Because the accumulation of ABA is an early event after the onset of drought stress, it has been postulated that ABA acts to coordinate the plant's response to water deficit (16). These responses include the closure of stomata, resulting in a limitation of the transpiration rate, a decrease in the water potential of the plant, and decreased photosynthesis (2). Changes in gene expression have been observed after periods of water deficit as indicated by the accumulation of novel polypeptides (3,12). In addition, a number of ABA-regulated genes have been isolated and characterized (for review, see ref. 32). Whereas the majority of these genes are expressed in embryos of developing seeds when the levels of ABA also rise, a few are also expressed in the wilting vegetative portions of the plant.

NaCI Reduces Indole-3-Acetic Acid Levels in the Roots of Tomato Plants Independent of Stress-Induced Abscisic Acid

“…The response to salt stress in plants often mimics the symptoms associated with temperature stress and water deficit. Drought, PEG-mediated water deficit, NaCl, and cold stress induced a 2-to 4-fold increase in the ABA content of tomato leaves (Plant et al, 1991). In this same study, the le16 gene of tomato induced by drought, low temperature, and ABA also was induced by NaCl.…”

Molecular Responses to Water Deficit

“…This DNA sequence is fourtd in many genes that are expressed during seed developmen t and in response to ABA application. However, it is not found in a11 genes that are in the ABAlrequiring category; for exarnple, lel6, a gene expressed in wild-type tomato but not $1 the ABA-deficient mutant, does ~ not contain a consensus ABRE (Plant et al, 1991). Recently, Michel et ai.…”

“…Another stress-induced protein is in a family reported to have antifungal activity. Nonspecific lipid transfer proteins are induced by drought (Plant et al, 1991;Torres-Schumann et al, 1992) and low-temperature stress (Hughes et al, 1992). Proteins in this class have been shown to transfer lipids in vitro, and they also inhibit fungal hypha growth (Terras et al, 1992).…”

Light Moderates the Induction of Phosphoenolpyruvate Carboxylase by NaCl and Abscisic Acid in Mesembryanthemum crystallinum

“…2, arrow). Two (1,12). Because incandescent light contributes energy in both the red and far red range, further studies would be needed to precisely determine the spectral response properties of PEPCase induction in the ice plant.…”