TcMYB8, a R3-MYB Transcription Factor, Positively Regulates Pyrethrin Biosynthesis in Tanacetum cinerariifolium

MYB proteins: Versatile regulators of plant development, stress responses, and secondary metabolite biosynthetic pathways

MYB proteins are ubiquitous in nature, regulating key aspects of plant growth and development. Although MYB proteins are known for regulating genes involved in secondary metabolite biosynthesis, particularly phenylpropanoids, their roles in terpenoid, glucosinolate, and alkaloid biosynthesis remain less understood. This review explores the structural and functional differences between activator and repressor MYB proteins along with their roles in plant growth, development, stress responses, and secondary metabolite production. MYB proteins serve as central hubs in protein-protein interaction networks that regulate expression of numerous genes involved in the adaptation of plants to varying environmental conditions. Thus, we also highlight key interacting partners of MYB proteins and their roles in these adaptation mechanisms. We further discuss the mechanisms regulating MYB proteins, including autoregulation, epigenetics, and post-transcriptional and post-translational modifications. Overall, we propose MYB proteins as versatile regulators for improving plant traits, stress responses, and secondary metabolite production.

Effects of elicitors from culture filtrate of Fusarium solani CL105 on flavonoid production of Scutellaria baicalensis calli

Introduction

Endophytic fungi can promote secondary metabolite accumulation in medicinal plants. Previously, we observed that the culture filtrate of Fusarium solani CL105 promoted flavonoid production in Scutellaria baicalensis calli. However, the active ingredients and mechanisms associated with this secondary metabolite accumulation remain unclear.

Methods

This study evaluates the effects of different elicitors from the culture filtrate of F. solani CL105 namely, exopolysaccharide (EPS), exoprotein (EP), and other parts (OP), on the flavonoid production in S. baicalensis calli by HPLC. Subsequently, the underlying mechanism of EPS induced flavonoid production in S. baicalensis calli was revealed by transcriptomics and RT-PCR.

Results and discussion

The results indicated a significant increase in flavonoid production in S. baicalensis calli following treatment with EPS. Baicalin (1.40 fold), wogonoside (1.91 fold), and wogonin (2.76 fold) were most significantly up-regulated compared with the control. Transcriptome analysis further revealed up-regulation of key enzyme genes (CHS, CHI, FNS, and F6H) involved in flavonoid synthesis after 5 days of EPS treatment. Moreover, the expression of GA2ox and CYP707A-genes involved in gibberellin acid (GA) and abscisic acid biosynthesis (ABA), respectively-were significantly up-regulated. The expression levels of certain transcription factors, including MYB3, MYB8, and MYB13, were also significantly higher than in controls. Our results indicated that EPS was a main active elicitor involved in promoting flavonoid production in S. baicalensis calli. We postulated that EPS might stimulate the expression of MYB3, MYB8, MYB13, GA2ox, and CYP707A, leading to markedly upregulated CHS, CHI, FNS, and F6H expression levels, ultimately promoting flavonoid synthesis. This study provides a novel avenue for large-scale in vitro production of flavonoids in S. baicalensis.

The Ginkgo biloba microRNA160-ERF4 module participates in terpene trilactone biosynthesis

Terpene trilactones (TTLs) are important secondary metabolites in ginkgo (Ginkgo biloba); however, their biosynthesis gene regulatory network remains unclear. Here, we isolated a G. biloba ethylene response factor 4 (GbERF4) involved in TTL synthesis. Overexpression of GbERF4 in tobacco (Nicotiana tabacum) significantly increased terpenoid content and upregulated the expression of key enzyme genes (3-hydroxy-3-methylglutaryl-CoA reductase [HMGR], 3-hydroxy-3-methylglutaryl-CoA synthase [HMGS], 1-deoxy-D-xylulose-5-phosphate reductoisomerase [DXR], 1-deoxy-D-xylulose-5-phosphate synthase [DXS], acetyl-CoA C-acetyltransferase [AACT], and geranylgeranyl diphosphate synthase [GGPPS]) in the terpenoid pathway in tobacco, suggesting that GbERF4 functions in regulating the synthesis of terpenoids. The expression pattern analysis and previous microRNA (miRNA) sequencing showed that gb-miR160 negatively regulates the biosynthesis of TTLs. Transgenic experiments showed that overexpression of gb-miR160 could significantly inhibit the accumulation of terpenoids in tobacco. Targeted inhibition and dual-luciferase reporter assays confirmed that gb-miR160 targets and negatively regulates GbERF4. Transient overexpression of GbERF4 increased TTL content in G. biloba, and further transcriptome analysis revealed that DXS, HMGS, CYPs, and transcription factor genes were upregulated. In addition, yeast 1-hybrid and dual-luciferase reporter assays showed that GbERF4 could bind to the promoters of the HMGS1, AACT1, DXS1, levopimaradiene synthase (LPS2), and GGPPS2 genes in the TTL biosynthesis pathway and activate their expression. In summary, this study investigated the molecular mechanism of the gb-miR160-GbERF4 regulatory module in regulating the biosynthesis of TTLs. It provides information for enriching the understanding of the regulatory network of TTL biosynthesis and offers important gene resources for the genetic improvement of G. biloba with high contents of TTLs.

Genome-Wide Identification and Expression Pattern of MYB Family Transcription Factors in Erianthus fulvus

MYB family genes have many functions and are widely involved in plant abiotic-stress responses. Erianthus fulvus is an important donor material for stress-resistance genes in sugarcane breeding. However, the MYB family genes in E. fulvus have not been systematically investigated. In this study, 133 EfMYB genes, including 48 Ef1R-MYB, 84 EfR2R3-MYB and 1 Ef3R-MYB genes, were identified in the E. fulvus genome. Among them, the EfR2R3-MYB genes were classified into 20 subgroups. In addition, these EfMYB genes were unevenly distributed across 10 chromosomes. A total of 4 pairs of tandemly duplicated EfMYB genes and 21 pairs of segmentally duplicated EfMYB genes were identified in the E. fulvus genome. Protein-interaction analysis predicted that 24 EfMYB proteins had potential interactions with 14 other family proteins. The EfMYB promoter mainly contains cis-acting elements related to the hormone response, stress response, and light response. Expression analysis showed that EfMYB39, EfMYB84, and EfMYB124 could be significantly induced using low-temperature stress. EfMYB30, EfMYB70, EfMYB81, and EfMYB101 responded positively to drought stress. ABA treatment significantly induced EfMYB1, EfMYB30, EfMYB39, EfMYB84, and EfMYB130. All nine genes were induced using MeJA treatment. These results provide comprehensive information on EfMYB genes and can serve as a reference for further studies of gene function.

TcbHLH14 a Jasmonate Associated MYC2-like Transcription Factor Positively Regulates Pyrethrin Biosynthesis in Tanacetum cinerariifolium

Natural pyrethrins have high application value, and are widely used as a green pesticide in crop pest prevention and control. Pyrethrins are mainly extracted from the flower heads of Tanacetum cinerariifolium; however, the natural content is low. Therefore, it is essential to understand the regulatory mechanisms underlying the synthesis of pyrethrins through identification of key transcription factors. We identified a gene encoding a MYC2-like transcription factor named TcbHLH14 from T. cinerariifolium transcriptome, which is induced by methyl jasmonate. In the present study, we evaluated the regulatory effects and mechanisms of TcbHLH14 using expression analysis, a yeast one-hybrid assay, electrophoretic mobility shift assay, and overexpression/virus-induced gene silencing experiments. We found that TcbHLH14 can directly bind to the cis-elements of the pyrethrins synthesis genes TcAOC and TcGLIP to activate their expression. The transient overexpression of TcbHLH14 enhanced expression of the TcAOC and TcGLIP genes. Conversely, transient silencing of TcbHLH14 downregulated the expression of TcAOC and TcGLIP and reduced the content of pyrethrins. In summary, these results indicate that the potential application of TcbHLH14 in improving the germplasm resources and provide a new insight into the regulatory network of pyrethrins biosynthesis of T. cinerariifolium to further inform the development of engineering strategies for increasing pyrethrins contents.