Calmodulin and Its Interactive Proteins Participate in Regulating the Explosive Growth of Alexandrium pacificum (Dinoflagellate)

Identification and characterisation of taste-enhancing peptides from oysters (Crassostrea gigas) via the Maillard reaction

Oysters, which are flavourful edible marine products, have been utilised to produce Maillard reaction products (MRPs), which contribute to saltiness enhancement. Here, the molecular weight distribution, free amino acids, and taste characteristics of MRPs were analysed, while ultraviolet light was used to observe the Maillard reaction. Both thermal degradation and cross-linking reactions occur during the Maillard reaction. When the Maillard reaction time was 90 min, the saltiness, umami, and richness of the MRPs peaked, however bitterness reached its lowest value. Moreover, at an MRP concentration of 1.5 mg/mL, salts were reduced by 35.71% in a 3 mg/mL sodium chloride solution without reducing saltiness, based on sensory evaluation. Glycation sites of the MRPs, which are crucial for saltiness enhancement and derived from a variety of protein sources, were determined using nano-HPLC-MS/MS analysis. Our study establishes the foundation for preparing salt-enhancing peptides, accelerating the popularisation of oyster-derived flavouring agents.

Identification of epigenetic histone modifications and analysis of histone lysine methyltransferases in Alexandrium pacificum

Alexandrium pacificum is a toxic dinoflagellate that can cause harmful algal blooms (HABs). The molecular mechanisms of HABs are still poorly understood, especially at the epigenetics level. Organism growth and metabolic processes are affected by histone modifications, an important mode of epigenetic regulation. In this study, various types of modifications, including methylation, acetylation, ubiquitination, and phosphorylation in A. pacificum cells were identified by using pan-antibodies, mass spectrometry, and an H3 modification multiplex assay kit. The modification abundance of H3K4me2 and H3K27me3 of A. pacificum varied under different growth conditions detected by Western blots. A class of SET domain genes (SDGs) encoding histone lysine methyltransferase was analyzed. A total of 179 SDG members were identified in A. pacificum, of which 53 sequences encoding complete proteins were classified into three categories by phylogenetic analysis, conserved domains and motifs analysis. Expression analysis and real-time polymerase chain reaction validation showed that the expressions of some SDGs were significantly influenced by light, nitrogen, phosphorus and manganese supplements. The results revealed that histone lysine methylation played an important role in responding to HABs inducing conditions. This study provided useful information for the further exploration of the role and regulatory mechanism of SDGs in the rapid growth of A. pacificum.

Establishment and preliminary study of electrophysiological techniques in a typical red tide species

Electrophysiology studies the electrical properties of cells and tissues including bioelectrical signals and membrane ion channel activities. As an important means to reveal ion channel related physiological functions and the underlying mechanisms, electrophysiological techniques have been widely used in studies of animals, higher plants and algae that are closely related to higher plants. However, few electrophysiological studies have been carried out in red tide organisms, especially in dinoflagellates, which is mainly due to the complex surface structure of dinoflagellate amphiesma. In this study, the surface amphiesma of Alexandrium pacificum, a typical red tide species, was removed by centrifugation, low-temperature treatment and enzymatic treatment. In all three treatments, low-temperature treatment with 4 °C for 2 h had high ecdysis rate and high fixation rate, and the treated cells were easy to puncture, so low-temperature treatment was used as a preprocessing treatment for subsequent current recording. Acquired protoplasts of A. pacificum were identified by calcofluor fluorescence and immobilized by poly-lysine. A modified "puncture" single-electrode voltage-clamp recording was first applied to dinoflagellates, and voltage-gated currents, which had the characteristics of outward K⁺ current and inward Cl^- current, were recorded and confirmed by ion replacement, indicating the voltage-gated currents were mixed. This method can be used as a technical basis for the electrophysiological study of dinoflagellates and provides a new perspective for the study of stress tolerance, red tide succession, and the regulation of physiological function of dinoflagellates.