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High Temperature Induces Expression of Tobacco Transcription Factor NtMYC2a to Regulate Nicotine and JA Biosynthesis.

ABSTRACT: Environmental stress elevates the level of jasmonic acid (JA) and activates the biosynthesis of nicotine and related pyridine alkaloids in tobacco (Nicotiana tabacum L.) by up-regulating the expression of putrescine N-methyltransferase 1 (NtPMT1), which encodes a putrescine N-methyl transferase that catalyzes nicotine formation. The JA signal suppressor JASMONATE ZIM DOMAIN 1 (NtJAZ1) and its target protein, NtMYC2a, also regulate nicotine biosynthesis; however, how these proteins interact to regulate abiotic-induced nicotine biosynthesis is poorly understood. In this study, we found that high-temperature (HT) treatment activated transcription of NtMYC2a, which subsequently stimulated the transcription of genes associated with JA biosynthesis, including Lipoxygenase (LOX), Allene oxide synthase (AOS), Allene oxide cyclase (AOC), and 12-oxophytodienodate reductase (OPR). Overexpression of NtMYC2a increased nicotine biosynthesis by enhancing its binding to the promoter of NtPMT1. Overexpression of either NtJAZ1 or proteasome-resistant NtJAZ1?C suppressed nicotine production under normal conditions, but overexpression only of the former resulted in low levels of nicotine under HT treatment. These data suggest that HT induces NtMYC2a accumulation through increased transcription to activate nicotine synthesis; meanwhile, HT-induced NtMYC2a can activate JA synthesis to promote additional NtMYC2a activity by degrading NtJAZ1 at the post-transcriptional level.

SUBMITTER: Yang L

PROVIDER: S-EPMC5081390 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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High Temperature Induces Expression of Tobacco Transcription Factor NtMYC2a to Regulate Nicotine and JA Biosynthesis.

Yang Liming L Li Junying J Ji Jianhui J Li Ping P Yu Liangliang L Abd Allah Elsayed F EF Luo Yuming Y Hu Liwei L Hu Xiangyang X

Frontiers in physiology 20161027

Environmental stress elevates the level of jasmonic acid (JA) and activates the biosynthesis of nicotine and related pyridine alkaloids in tobacco (Nicotiana tabacum L.) by up-regulating the expression of putrescine N-methyltransferase 1 (NtPMT1), which encodes a putrescine N-methyl transferase that catalyzes nicotine formation. The JA signal suppressor JASMONATE ZIM DOMAIN 1 (NtJAZ1) and its target protein, NtMYC2a, also regulate nicotine biosynthesis; however, how these pr ...[more]

PMID: 27833561

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Project description:Traditional breeding and molecular approaches have been used to develop tobacco varieties with reduced nicotine and secondary alkaloid levels. However, available low-alkaloid tobacco varieties have impaired leaf quality likely due to the metabolic consequences of nicotine biosynthesis downregulation. Recently, we found evidence that the unbalanced crosstalk between nicotine and polyamine pathways is involved in impaired leaf ripening of a low-alkaloid (LA) Burley 21 line having a mutation at the Nic1 and Nic2 loci, key biosynthetic regulators of nicotine biosynthesis. Since the Nic1 and Nic2 loci are comprised of several genes, all phenotypic changes seen in LA Burley 21 could be due to a mixture of genetics-based responses. Here, we investigated the commercial burley variety TN90 LC and its transgenic versions with only one downregulated gene, either putrescine methyl transferase (PMT-RNAi) or PR50-protein (PR50-RNAi). Nicotine levels of cured lamina of TN90 LC, TN90 PMT-RNAi and TN90 PR50-RNAi, were 70.5 ± 3.8, 2.4 ± 0.5, and 6.0 ± 1.1 mg/g dry weight, respectively. Low-alkaloid transgenic lines showed delayed leaf maturation and impaired leaf quality. We analyzed polyamine contents and ripening markers in wild-type TN90 control plants (WT) and the two transgenic lines. The ripening markers revealed that the PMT-RNAi line showed the most pronounced impaired leaf maturation phenotype at harvest, characterized by higher chlorophyll (19%) and glucose (173%) contents and more leaf mesophyll cells per area (25%), while the ripening markers revealed that maturation of PR50-RNAi plants was intermediate between PMT-RNAi and WT lines. Comparative polyamine analyses showed an increase in free and conjugated polyamines in roots of both transgenic lines, this being most pronounced in the PMT-RNAi plants. For PMT-RNAi plants, there were further perturbations of polyamine content in the leaves, which mirrored the general phenotype, as PR50-RNAi transgenic plants looked more similar to the WT than PMT-RNAi transgenic plants. Activity of ornithine decarboxylase, the enzyme that catalyzes the committing step of polyamine biosynthesis, was significantly higher in roots and mature leaves of PMT-RNAi plants in comparison to WT, while there was no increase observed for arginine decarboxylase. Treatment of both transgenic lines with polyamine biosynthesis inhibitors decreased the polyamine content and ameliorated the phenotype, confirming the intricate interplay of polyamine and nicotine biosynthesis in tobacco and the influence of this interplay on leaf ripening.

Dataset Information

High Temperature Induces Expression of Tobacco Transcription Factor NtMYC2a to Regulate Nicotine and JA Biosynthesis.

Publications

High Temperature Induces Expression of Tobacco Transcription Factor NtMYC2a to Regulate Nicotine and JA Biosynthesis.

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