Abstract
Betaine, a non-toxic osmoprotectant, is believed to accumulate considerably in plants under stress conditions to maintain the osmotic pressure and promote a variety of processes involved in growth and development. Phosphoethanolamine N-methyltransferase (PEAMT), a key enzyme for betaine synthesis, is reported to be regulated by its upstream promoter. In the present investigation, by using the transgenic approach, a 1048 bp long promoter region of ZmPEAMT gene from Zea mays was cloned and functionally characterized in tobacco. Computational analysis affirmed the existence of abiotic stress responsive cis-elements like ABRE, MYC, HST, LST etc., as well as pathogen, wound and phytohormone responsive motifs. For transformation in tobacco, four 5′-deletion constructs of 826 bp (P2), 642 bp (P3), 428 bp (P4) and 245 bp (P5) were constructed from the 1048 bp (P1) promoter fragment. The transgenic plants generated through a single event exhibited a promising expression of GUS reporter protein in the leaf tissues of treated with salt, drought, oxidative and cold stress as well as control plants. The GUS expression level progressively reduced from P1 to P5 in the leaf tissues, whereas a maximal expression was observed with the P3 construct in the leaves of control plants. The expression of GUS was noted to be higher in the leaves of osmotically- or salt-treated transgenic plants than that in the untreated (control) plants. An effective expression of GUS in the transgenic plants manifests that this promoter can be employed for both stress-inducible and constitutive expression of gene(s). Due to this characteristic, this potential promoter can be effectively used for genetic engineering of several crops.
Highlights
In a wide variety of plant cells, choline is a vital osmoprotectant that plays an important role in plant stress resistance by maintaining the optimal cellular activities [1]
The predicted core promoter elements included TATA-box starting from 208th bp upstream to the ATG codon and CAAT-box, which may play a key role in transcription initiation for ZmPEAMT
The model of ZmPEAMT promoter action in transgenic tobacco assumes that abiotic stresses improve the binding of stress-related transcription factors and stress response promoter elements and it increase the activity of ZmPEAMT promoter, which correlate with the induction of GUS expression
Summary
In a wide variety of plant cells, choline is a vital osmoprotectant that plays an important role in plant stress resistance by maintaining the optimal cellular activities [1]. Phosphoethanolamine N-methyltransferase (PEAMT) is a rate-limiting key enzyme for choline synthesis, and its main function is to catalyze the methylation of phosphoethanolamine producing phosphocholine. The latter can produce choline and phosphatidic acid under the hydrolysis of phosphocholine phosphatase, which mainly occurs in plants belonging to family Chenopodiaceae [2]. S-adenosyl-L-methionine-dependent methyltransferase domains, the N-terminal (MT1) and the C-terminal (MT2) domains. Each domain contains four motifs, which could catalyze the choline synthesis. For phosphocholine (P-Cho) production, the first methylation step of phosphoethanolamine (P-Etn) to phosphomonomethylethanolamine (P-MMEtn) is catalyzed by the MT1 domain, while, the second domain (MT2) catalyzes the second methylation reaction of P-MMEtn to P-Cho [4]
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