Major developmental transitions in multicellular organisms are driven by steroid hormones. In insects, these, together with juvenile hormone (JH), control development, metamorphosis, reproduction and aging, and are also suggested to play an important role in caste differentiation of social insects. Here, we aimed to determine how EcR transcription and ecdysteroid titers are related during honeybee postembryonic development and what may actually be the role of EcR in caste development of this social insect. In addition, we expected that knocking-down EcR gene expression would give us information on the participation of the respective protein in regulating downstream targets of EcR. We found that in Apis mellifera females, EcR-A is the predominantly expressed variant in postembryonic development, while EcR-B transcript levels are higher in embryos, indicating an early developmental switch in EcR function. During larval and pupal stages, EcR-B expression levels are very low, while EcR-A transcripts are more variable and abundant in workers compared to queens. Strikingly, these transcript levels are opposite to the ecdysteroid titer profile. 20-hydroxyecdysone (20E) application experiments revealed that low 20E levels induce EcR expression during development, whereas high ecdysteroid titers seem to be repressive. By means of RNAi-mediated knockdown (KD) of both EcR transcript variants we detected the differential expression of 234 poly-A+ transcripts encoding genes such as CYPs, MRJPs and certain hormone response genes (Kr-h1 and ftz-f1). EcR-KD also promoted the differential expression of 70 miRNAs, including highly conserved ones (e.g., miR-133 and miR-375), as well honeybee-specific ones (e.g., miR-3745 and miR-3761). Our results put in evidence a broad spectrum of EcR-controlled gene expression during postembryonic development of honeybees, revealing new facets of EcR biology in this social insect.

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Ftz‐f1 is an orphan member of the nuclear hormone receptor superfamily. A 20‐hydroxyecdysone pulse allows ftz‐f1 gene expression, which then regulates the activity of downstream genes involved in major developmental progression events. In honeybees, the expression of genes like vitellogenin (vg), prophenoloxidase and juvenile hormone‐esterase during late pharate‐adult development is known to be hormonally controlled in both queens and workers by increasing juvenile hormone (JH) titres in the presence of declining levels of ecdysteroids. Since Ftz‐f1 is known for mediating intracellular JH signalling, we hypothesized that ftz‐f1 could mediate JH action during the pharate‐adult development of honeybees, thus controlling the expression of these genes. Here, we show that ftz‐f1 has caste‐specific transcription profiles during this developmental period, with a peak coinciding with the increase in JH titre, and that its expression is upregulated by JH and downregulated by ecdysteroids. RNAi‐mediated knock down of ftz‐f1 showed that the expression of genes essential for adult development (e.g. vg and cuticular genes) depends on ftz‐f1 expression. Finally, a double‐repressor hypothesis‐inspired vg gene knock‐down experiment suggests the existence of a positive molecular loop between JH, ftz‐f1 and vg.

IntroductionBy mid-century, global atmospheric carbon dioxide concentration ([CO2]) is predicted to reach 600 μmol mol−1 with global temperatures rising by 2 °C. Rising [CO2] and temperature will alter the growth and productivity of major food and forage crops across the globe. Although the impact is expected to be greatest in tropical regions, the impact of climate-change has been poorly studied in those regions.ObjectivesThis experiment aimed to understand the effects of elevated [CO2] (600 μmol mol−1) and warming (+ 2 °C), singly and in combination, on Panicum maximum Jacq. (Guinea grass) metabolite and transcript profiles.MethodsWe created a de novo assembly of the Panicum maximum transcriptome. Leaf samples were taken at two time points in the Guinea grass growing season to analyze transcriptional and metabolite profiles in plants grown at ambient and elevated [CO2] and temperature, and statistical analyses were used to integrate the data.ResultsElevated temperature altered the content of amino acids and secondary metabolites. The transcriptome of Guinea grass shows a clear time point separations, with the changes in the elevated temperature and [CO2] combination plots.ConclusionField transcriptomics and metabolomics revealed that elevated temperature and [CO2] result in alterations in transcript and metabolite profiles associated with environmental response, secondary metabolism and stomatal function. These metabolic responses are consistent with greater growth and leaf area production under elevated temperature and [CO2]. These results show that tropical C4 grasslands may have unpredicted responses to global climate change, and that warming during a cool growing season enhances growth and alleviates stress.Electronic supplementary materialThe online version of this article (10.1007/s11306-019-1511-8) contains supplementary material, which is available to authorized users.