The ability to navigate long distances is essential for many animals to locate shelter, food, and breeding grounds. Magnetic sense has evolved in various migratory and homing species to orient them based on the geomagnetic field. A highly conserved iron-sulfur cluster assembly protein IscA is proposed as an animal magnetoreceptor (MagR). Iron-sulfur cluster binding is also suggested to play an essential role in MagR magnetism and is thus critical in animal magnetoreception. In the current study, we provide evidence for distinct iron binding and iron-sulfur cluster binding in MagR in pigeons, an avian species that relies on the geomagnetic field for navigation and homing. Pigeon MagR showed significantly higher total iron content from both iron- and iron-sulfur binding. Y65 in pigeon MagR was shown to directly mediate mononuclear iron binding, and its mutation abolished iron-binding capacity of the protein. Surprisingly, both iron binding and iron-sulfur binding demonstrated synergistic effects, and thus appear to be integral and indispensable to pigeon MagR magnetism. These results not only extend our current understanding of the origin and complexity of MagR magnetism, but also imply a possible molecular explanation for the huge diversity in animal magnetoreception.

Dendrobium officinale is both a traditional herbal medicine and a plant of high ornamental and medicinal value. Alkaloids, especially terpenoid indole alkaloids (TIAs), with pharmacological activities are present in the tissues of D. officinale. A number of genes involved in alkaloid biosynthetic pathways have been identified. However, the regulatory mechanisms underlying the precursor and methyl jasmonate (MeJA)-induced accumulation of alkaloids in D. officinale are poorly understood. In this study, we collected D. officinale protocorm-like bodies (PLBs) and treated them with TIA precursors (tryptophan and secologanin) and MeJA for 0 (T0), 4 (T4) and 24 h (T24); we also established control samples (C4 and C24). Then, we measured the total alkaloid content of the PLBs and performed transcriptome sequencing using the Illumina HiSeq 2,500 system. The total alkaloid content increased significantly after 4 h of treatment. Go and KEGG analysis suggested that genes from the TIA, isoquinoline alkaloid, tropane alkaloid and jasmonate (JA) biosynthetic pathways were significantly enriched. Weighted gene coexpression network analysis (WGCNA) uncovered brown module related to alkaloid content. Six and seven genes related to alkaloid and JA bisosynthetic pathways, respectively, might encode the key enzymes involved in alkaloid biosynthesis of D. officinale. Moreover, 13 transcription factors (TFs), which mostly belong to AP2/ERF, WRKY, and MYB gene families, were predicted to regulate alkaloid biosynthesis. Our data provide insight for studying the regulatory mechanism underlying TIA precursor and MeJA-induced accumulation of three types of alkaloids in D. officinale.

Amplitude-modulated bursting (AMB), characterized by oscillations appearing in the envelope of the active phase of bursting, is a novel class of bursting rhythms reported recently. The present paper aims to report a simple and effective method, i.e., the multiple-frequency slow parametric modulation (MFSPM) method, for obtaining such a bursting pattern. We show that the MFSPM can be well controlled so that it may exhibit multiple continuous ups and downs in the active area. Then, the amplitude of the traced active state alternates between increases and decreases accordingly, which leads to oscillations in the envelope of the active phase, and AMB is thus created. Based on this, the route to AMB by the MFSPM is presented. The validity of the approach is demonstrated by several examples. The proposed approach does not depend on specific systems or bifurcations and thus is a general method.

The pulse-shaped explosion (PSE), characterized by the pulse-shaped quantitative of system solutions varying dramatically, is a special route to bursting oscillations reported recently. This paper reports interesting dynamical behaviors related to the PSE of equilibria, and based on that, the complex bursting dynamics is investigated in a van der Pol–Mathieu–Duffing system with multiple-frequency slow-varying excitations. We find that bifurcations can be observed in a narrow parameter interval within PSE. We also show that two groups of bifurcations are symmetrically arranged on both sides of PSE, and each of which determines a different bursting part. Based on this, two compound bursting patterns, i.e. compound Hopf/Hopf bursting oscillation and compound subHopf/fold cycle bursting oscillation, and a novel type of relaxation oscillation (bursting oscillation of point/point) independent of bifurcations, are revealed. Our results enrich the knowledge of dynamical behaviors related to PSE as well as the possible routes to complex bursting dynamics.

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