Post-transcriptional regulation of hormone synthesis

Extensive post-transcriptional regulation revealed by integrative transcriptome and proteome analyses in salicylic acid-induced flowering in duckweed (Lemna gibba)

Duckweed is an aquatic model plant with tremendous potential in industrial and agricultural applications. Duckweed rarely flowers which significantly hinders the resource collection and heterosis utilization. Salicylic acid (SA) can significantly induce duckweed to flower; however, the underlying regulatory mechanisms remain largely unknown. In this work, transcriptome and proteome were conducted in parallel to examine the expression change of genes and proteins in Lemna gibba under SA treatment. A high-quality reference transcriptome was generated using Iso-Seq strategy, yielding 42,281 full-length transcripts. A total of 422, 423, and 417 differentially expressed genes (DEGs), as well as 213, 51, and 92 differentially expressed proteins (DEPs), were identified at flower induction, flower initiation, and flowering stages by ssRNA-seq and iTRAQ methods. Most DEGs and DEPs were only regulated at either the transcriptomic or proteomic level. Additionally, DEPs exhibited low expression correlations with the corresponding mRNAs, suggesting that post-transcriptional regulation plays a pivotal role in SA-induced flowering in L. gibba. Specifically, the genes related to photosynthesis, stress, and hormone metabolism were mainly regulated at the mRNA level, those associated with mitochondrial electron transport / ATP synthesis, nucleotide synthesis, and secondary metabolism were regulated at the protein level, while those related to redox metabolism were regulated at the mRNA and/or protein levels. The post-transcriptional regulation of genes relevant to hormone synthesis, transcription factors, and flowering was also extensively analyzed and discussed. This is the first study of integrative transcriptomic and proteomic analyses in duckweed, providing novel insights of post-transcriptional regulation in SA-induced flowering of L. gibba.

Daily melatonin injections induce cytological changes in pars tuberalis-specific cells similar to short photoperiod

Hypophyseal pars tuberalis (PT)-specific cells are known to exhibit remarkable seasonal changes in morphology especially in photoperiodic animals like the Djungarian hamster Phodopus sungorus. Their high density of melatonin-receptors leads to the supposition that fluctuations in circulating melatonin levels are a crucial factor for the morphological alterations induced by photoperiodic signals. To prove this hypothesis the nocturnal elevation of melatonin in long photoperiods was prolonged by late afternoon administration of melatonin. We investigated whether this treatment induces cytological changes usually observable under short photoperiod. Electron microscopy revealed that in contrast to hamsters maintained in long photoperiods PT-specific cells of hamsters injected with melatonin or those kept in short photoperiods appear inactive, containing a relatively high number of secretory granules, sparse endoplasmatic reticulum, irregularly outlined and invaginated cell nuclei and a high amount of glycogen. Furthermore immunoreactivity for the common alpha-chain of glycoprotein hormones and beta-TSH was significantly weaker in hamsters kept in short photoperiods or daily injected with melatonin than untreated or vehicle injected controls in long photoperiod. These results demonstrate that an exogenous prolongation of the elevated nocturnal melatonin levels causes a similar morphological appearance of PT-specific cells as observed in short photoperiods. It is tempting to speculate that the melatonin signal is a direct 'Zeitgeber' for the transduction of photoperiodic information to the secretory activity in this cell type.

Thyroid hormone modulates apolipoprotein-AI gene expression at the post-transcriptional level in Hep G2 cells

Hyperthyroidism is associated with elevated plasma levels of apolipoprotein AI (apo AI). We have examined the effects of 3,3',-5-triiodothyronine on apo AI mRNA, transcription run-on activity, apo AI mRNA half-life, and the rate of protein synthesis in Hep G2 cells, to understand the molecular mechanism by which thyroid hormone regulates apo AI gene expression. Incubation with thyroid hormone increased the apo AI and apo AII mRNA concentrations twofold. Cycloheximide alone caused a significant increase in apo AI mRNA. Nuclear run-on assays indicate that thyroid hormone did not change the rate of the apo AI gene transcription at 6, 12 or 24 h, showing that thyroid hormone did not modulate apo AI gene transcription. Kinetic studies performed in the presence of actinomycin D showed that the half-life of apo AI mRNA was increased 2-3-fold by thyroid hormone over control cells. Thyroid hormone did not change the incorporation of [35S]methionine into immunoprecipitable apo AI. Pulse-chase experiments demonstrated that there was no change in the secretion and degradation rates of labeled apo AI in response to T3. This suggests that thyroid hormone does not affect the catabolism of apo AI (degradation or/and uptake) and that translation control strongly influences the regulation of apo AI gene expression. The stabilization of apo AI mRNA by thyroid hormone and its role in translation remain to be elucidated.