Transcriptional regulation of flavonol biosynthesis in plants.

Flavonols are a class of flavonoids that play a crucial role in regulating plant growth and promoting stress resistance. They are also important dietary components in horticultural crops due to their benefits for human health. In past decades, research on the transcriptional regulation of flavonol biosynthesis in plants has increased rapidly. This review summarizes recent progress in flavonol-specific transcriptional regulation in plants, encompassing characterization of different categories of transcription factors (TFs) and microRNAs as well as elucidation of different transcriptional mechanisms, including direct and cascade transcriptional regulation. Direct transcriptional regulation involves TFs, such as MYB, AP2/ERF, and WRKY, which can directly target the key flavonol synthase gene or other early genes in flavonoid biosynthesis. In addition, different regulation modules in cascade transcriptional regulation involve microRNAs targeting TFs, regulation between activators, interaction between activators and repressors, and degradation of activators or repressors induced by UV-B light or plant hormones. Such sophisticated regulation of the flavonol biosynthetic pathway in response to UV-B radiation or hormones may allow plants to fine-tune flavonol homeostasis, thereby balancing plant growth and stress responses in a timely manner. Based on orchestrated regulation, molecular design strategies will be applied to breed horticultural crops with excellent health-promoting effects and high resistance.

Synergistic actions of three MYB transcription factors underpins the high accumulation of myricetin in Morella rubra.

Flavonols are health-promoting bioactive compounds important for human nutrition, health, and plant defense. The transcriptional regulation of kaempferol and quercetin biosynthesis has been studied extensively, while little is known about the regulatory mechanisms underlying myricetin biosynthesis, which has strong antioxidant, anticancer, antidiabetic, and anti-inflammatory activities. In this study, the flavonol-specific MrMYB12 in Morella rubra preferred activating the promoter of flavonol synthase 2 (MrFLS2) (6.4-fold) rather than MrFLS1 (1.4-fold) and upregulated quercetin biosynthesis. Furthermore, two SG44 R2R3-MYB members, MrMYB5 and MrMYB5L, were identified by yeast one-hybrid library screening using the promoter of flavonoid 3',5'-hydroxylase (MrF3'5'H), and transcript levels of these R2R3-MYBs were correlated with accumulation of myricetin derivatives during leaf development. Dual-luciferase and electrophoretic mobility shift assays demonstrated that both MrMYB5 and MrMYB5L could bind directly to MYB recognition sequence elements in promoters of MrF3'5'H or MrFLS1 and activate their expression. Protein-protein interactions of MrMYB5 or MrMYB5L with MrbHLH2 were confirmed by yeast two-hybrid and bimolecular fluorescence complementation assays. MrMYB5L-MrbHLH2 showed much higher synergistic activation of MrF3'5'H or MrFLS1 promoters than MrMYB5-MrbHLH2. Studies with Arabidopsis thaliana homologs AtMYB5 and AtTT8 indicated that similar synergistic regulatory effects occur with promoters of MrF3'5'H or MrFLS1. Transient overexpression of MrMYB5L-MrbHLH2 in Nicotiana benthamiana induced a higher accumulation of myricetin derivatives (57.70 µg g-1 FW) than MrMYB5-MrbHLH2 (7.43 µg g-1 FW) when MrMYB12 was coexpressed with them. This study reveals a novel transcriptional mechanism regulating myricetin biosynthesis with the potential use for future metabolic engineering of health-promoting flavonols.

Correction: The novel leucine-rich repeat receptor-like kinase MRK1 regulates resistance to multiple stresses in tomato.

[This corrects the article DOI: 10.1093/hr/uhab088.].

A novel leucine-rich repeat receptor-like kinase MRK1 regulates resistance to multiple stresses in tomato.

Leucine-rich repeat receptor-like kinases (LRR-RLKs) are ubiquitous in higher plants, which act as receptors of extracellular signals to trigger multiple physiological processes. However, the functions of the majority of LRR-RLKs remain largely unknown, especially in tomato (Solanum lycopersicum L.). Here, we found that MRK1 (Multiple resistance-associated kinase 1), encoding a novel tomato LRR-RLK, was significantly induced either by temperature stresses or bacterial pathogen attacks. Knocking out MRK1 impaired the tolerance to both cold and heat stress, accompanied with the decrease in transcripts of master regulators C-repeat binding factor 1 (CBF1) and Heat shock transcription factor a-1a (HsfA1a), respectively. Additionally, mrk1 mutants were hypersensitive to Pseudomonas syringae pv. tomato DC3000 and Ralstonia solanacearum and compromised pattern-triggered immunity (PTI) responses as evidenced by decreased reactive oxygen species production and reduced upregulation of the PTI marker genes. Moreover, bimolecular fluorescence complementation, split-luciferase assay and coimmunoprecipitation supported the existence of complex formation between the MRK1, FLS2 and Somatic embryogenesis receptor kinase (SERK3A/SERK3B) in a ligand-independent manner. This work demonstrates that tomato MRK1 as a novel positive regulator of multiple stresses, which might be a potential breeding target to improve crop stress resistance.

High CO2 - and pathogen-driven expression of the carbonic anhydrase ßCA3 confers basal immunity in tomato.

Atmospheric CO2 concentrations exert a strong influence on the susceptibility of plants to pathogens. However, the mechanisms involved in the CO2 -dependent regulation of pathogen resistance are largely unknown. Here we show that the expression of tomato (Solanum lycopersicum) ß-CARBONIC ANHYDRASE 3 (ßCA3) is induced by the virulent pathogen Pseudomonas syringae pv. tomato DC3000. The role of ßCA3 in the high CO2 -mediated response in tomato and two other Solanaceae crops is distinct from that in Arabidopsis thaliana. Using ßCA3 knock-out and over-expression plants, we demonstrate that ßCA3 plays a positive role in the activation of basal immunity, particularly under high CO2 . ßCA3 is transcriptionally activated by the transcription factor NAC43 and is also post-translationally regulated by the receptor-like kinase GRACE1. The ßCA3 pathway of basal immunity is independent on stomatal- and salicylic-acid-dependent regulation. Global transcriptome analysis and cell wall metabolite measurement implicate cell wall metabolism/integrity in ßCA3-mediated basal immunity under both CO2 conditions. These data not only highlight the importance of ßCA3 in plant basal immunity under high CO2 in a well-studied susceptible crop-pathogen system, but they also point to new targets for disease management strategies in a changing climate.

Neoliberal Optimism: Applying Market Techniques to Global Health.

Global health and neoliberalism are becoming increasingly intertwined as organizations utilize markets and profit motives to solve the traditional problems of poverty and population health. I use field work conducted over 14 months in a global health technology company to explore how the promise of neoliberalism re-envisions humanitarian efforts. In this company's vaccine refrigerator project, staff members expect their investors and their market to allow them to achieve scale and develop accountability to their users in developing countries. However, the translation of neoliberal techniques to the global health sphere falls short of the ideal, as profits are meager and purchasing power remains with donor organizations. The continued optimism in market principles amidst such a non-ideal market reveals the tenacious ideological commitment to neoliberalism in these global health projects.