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 NtJAZ1ΔC 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.
Highlights
Tobacco (Nicotiana tabacum) generates an array of alkaloids that play essential roles in the plant defense response against herbivore and insect attack (Kessler and Baldwin, 2002; Steppuhn et al, 2004)
We found that HT treatment effectively enhanced nicotine biosynthesis in tobacco
Given that N-methyltransferase 1 (NtPMT1) is the key enzyme in the nicotine biosynthesis pathway (Shoji and Hashimoto, 2011; Zhang et al, 2012), we evaluated the effect of HT on NtPMT1 accumulation in tobacco roots using NtPMT1 antibody
Summary
Tobacco (Nicotiana tabacum) generates an array of alkaloids that play essential roles in the plant defense response against herbivore and insect attack (Kessler and Baldwin, 2002; Steppuhn et al, 2004). Nicotine is the main alkaloid produced by cultivated tobacco (N. tabacum L.), constituting ∼0.6–3% of the tobacco leaf dry weight. NtMYC2a Mediates Nicotine Biosynthesis arginine by way of putrescine. Putrescine is either metabolized to higher polyamines, such as spermidine and spermine, or conjugated with cinnamic acid derivatives or fatty acids in all higher plants; it is converted into N-methylputrescine in plants that produce nicotine or tropane alkaloids. After biosynthesis in the tobacco root, nicotine is translocated to the leaf via the xylem and stored in the leaf vacuole with the help of a tonoplast-localized transporter. Nicotine can be demethylated in both leaves and roots, but it is primarily demethylated in senescing leaves (Wagner et al, 1986; Chou and Kutchan, 1998).
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