Abstract
MYC2/3/4, known as a basic helix–loop–helix (bHLH) transcription factor, directly activate the genes involved in diverse plant development and secondary metabolites biosynthesis. In this study, we identified and cloned five MYC paralogs (BrMYC2/3-1/3-2/4-1/4-2) from Chinese cabbage (Brassica rapa ssp. pekinensis). In-silico analyses for the physicochemical properties suggested that BrMYC2/3-1/3-2/4-2/4-3 are unstable hydrophobic and acidic proteins, while BrMYC4-1 is an unstable hydrophobic and basic protein. BrMYC2/3/4 belong to the bHLH superfamily and are closely related to AthMYC2/3/4 orthologs that mediate the regulation of various secondary metabolites. It was demonstrated that BrMYC2/3/4-GFP fusion protein localized in the nucleus and expression levels of five BrMYC2/3/4 homologous genes all elevated relative to control (Ctrl). When expressed in Arabidopsis under the control of 35S promoter, each of the BrMYC2/3-1/3-2/4-1/4-2 transgenes differentially influenced root and shoot elongation, vegetative phase change, flowering time, plant height and tiller number after flowering, and seed production. Despite the variation of phenotypes between the transgenic lines, all the lines except for BrMYC4-2 exhibited shorter seed length, less seed weight, higher accumulation of glucosinolates (GSs), and resistance to Sclerotinia sclerotiorum than Ctrl. Notably, BrMYC2 overexpression (OE) line significantly reduced the lengths of root and hypocotyl, seed length, and weight, along with faster bolting time and strikingly higher accumulation of total GSs. Accumulation of GSs at the highest levels in the BrMYC2OE line conferred the highest resistance to S. sclerotiorum. Unlike BrMYC3OE and BrMYC4OE, BrMYC2OE stimulated the growth of plant height after fluorescence. The results of this study point to the BrMYC2 overexpression that may provide a beneficial effect on plant growth and development via plant resistance to the fungal pathogen.
Highlights
Myelocytomatosis proteins (MYCs) are key transcription factors (TFs) in the response pathway of jasmonic acid (JA) in plants (Xie et al, 2020)
The results showed that BrMYC2, BrMYC3-1, BrMYC3-2, and BrMYC4-2 have a conserved domain named basic helix–loop–helix (bHLH)-MYC_N superfamily; BrMYC2, BrMYC3-1, BrMYC3-2, and BrMYC4-1 have a conserved domain named bHLH_AtABAinducible bHLH-TYPE_like in the C-terminal region; and BrMYC4-3 contains a single domain named bHLH-MYC_N (Figure 1)
ABA-inducible bHLH-TYPE (AIB) is an abscisic acid (ABA)-inducible transcriptional repressor that negatively regulates JA signaling (Nakata et al, 2013). These domain features implicate that BrMYC2/3/4 belongs to the bHLH superfamily of TFs mediating the positive and negative regulation of plant development and various secondary metabolites synthesis
Summary
Myelocytomatosis proteins (MYCs) are key transcription factors (TFs) in the response pathway of jasmonic acid (JA) in plants (Xie et al, 2020). Glucosinolates are a group of secondary metabolites found in Brassicaceae family and are composed of β-D-thioglucose and sulfonated oxime moieties (Tiwari, 2018) They have received considerable interest because of their commercial properties of anti-cancer agents (Arumugam and Razis, 2018), bio-pesticides (Malka and Cheng, 2017), and flavor condiment (Burow et al, 2015). They are typically classified as aliphatic GS (from alanine, valine, leucine, isoleucine, or methionine), aromatic GS (from phenylalanine or tyrosine), or indole GS (from tryptophan) on the basis of their modified side chains (R) derived from amino acids through a long chain lengthening process and hydroxylation or oxidation (Rahimi and Rahmanpour, 2020)
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