Summary: Early responses of plants to environmental stress factors prevent damage but can delay growth and development in fluctuating conditions. Optimising these trade‐offs requires tunability of plant responsiveness to environmental signals. We have previously reported that Histone Deacetylase Complex 1 (HDC1), which interacts with multiple proteins in histone deacetylation complexes, regulates the stress responsiveness of Arabidopsis seedlings, but the underlying mechanism remained elusive. Here, we show that HDC1 attenuates transcriptome re‐programming in salt‐treated seedlings, and we identify two genes ( LEA and MAF5 ) that inhibit seedling establishment under salt stress downstream of HDC1. HDC1 attenuates their transcriptional induction by salt via a dual mechanism involving H3K9/14 deacetylation and H3K27 trimethylation. The latter, but not the former, was also abolished in a triple knockout mutant of the linker histone H1, which partially mimics the hypersensitivity of the hdc1‐1 mutant to salt stress. Although stress‐induced H3K27me3 accumulation required both H1 and HDC1, it was not fully recovered by complementing hdc1‐1 with a truncated, H1‐binding competent HDC1 suggesting other players or independent inputs. The combined findings reveal a dual brake function of HDC1 via regulating both active and repressive epigenetic marks on stress‐inducible genes. This natural ‘anti‐panic’ device offers a molecular leaver to tune stress responsiveness in plants.

Taraxacum kok-saghyz R. (Tks) is a promising alternative species to Hevea brasiliensis for production of high quality natural rubber (NR). A comparative transcriptome analysis of plants with differential production of NR will contribute to elucidate which genes are involved in the synthesis, regulation and accumulation of this natural polymer and could help to develop Tks into a rubber crop. We measured rubber content in the latex of 90 individual Tks plants from 9 accessions, observing a high degree of variability. We carried out de novo root transcriptome sequencing, assembly, annotation and comparison of gene expression of plants with the lower (LR plants) and the higher rubber content (HR plants). The transcriptome analysis also included one plant that did not expel latex, in principle depleted of latex transcripts. Moreover, the transcription of some genes well known to play a major role in rubber biosynthesis, was probed by qRT-PCR. Our analysis showed a high modulation of genes involved in the synthesis of NR between LR and HR plants, and evidenced that genes involved in sesquiterpenoids, monoterpenoids and phenylpropanoid biosynthesis are upregulated in LR plants. Our results show that a higher amount of rubber in the latex in HR plants is positively correlated with high expression levels of a number of genes directly involved in rubber synthesis showing that NR production is highly controlled at transcriptional level. On the other hand, lower amounts of rubber in LR plants is related with higher expression of genes involved in the synthesis of other secondary metabolites that, we hypothesize, may compete towards NR biosynthesis. This dataset represents a fundamental genomic resource for the study of Tks and the comprehension of the synthesis of NR and other biochemically and pharmacologically relevant compounds in the Taraxacum genus.

Taraxacum kok-saghyz (Tks), also known as the Russian dandelion, is a recognized alternative source of natural rubber quite comparable, for quality and use, to the one obtained from the so-called rubber tree, Hevea brasiliensis. In addition to that, Tks roots produce several other compounds, including inulin, whose use in pharmaceutical and dietary products is quite extensive. Histone-modifying genes (HMGs) catalyze a series of post-translational modifications that affect chromatin organization and conformation, which, in turn, regulate many downstream processes, including gene expression. In this study, we present the first analysis of HMGs in Tks. Altogether, we identified 154 putative Tks homologs: 60 HMTs, 34 HDMs, 42 HATs, and 18 HDACs. Interestingly, whilst most of the classes showed similar numbers in other plant species, including M. truncatula and A. thaliana, HATs and HMT-PRMTs were indeed more abundant in Tks. Composition and structure analysis of Tks HMG proteins showed, for some classes, the presence of novel domains, suggesting a divergence from the canonical HMG model. The analysis of publicly available transcriptome datasets, combined with spatial expression of different developmental tissues, allowed us to identify several HMGs with a putative role in metabolite biosynthesis. Overall, our work describes HMG genomic organization and sets the premises for the functional characterization of epigenetic modifications in rubber-producing plants.

Taraxacum kok-saghyz (Tks) is a promising plant species for natural rubber (NR) production and represents a model for studying NR biosynthesis in the Asteraceae family. The generation of transgenic plants overexpressing a gene of interest is a well-established strategy to investigate gene function and potential interactions. Here, we present a comprehensive workflow—from the construction of an overexpression vector to the generation, identification, and propagation of stable transgenic Tks lines. In addition, we describe a rapid and reliable method for quantifying NR content in transformed plants, providing essential phenotypic characterisation in this species.

Hydrogen is a key energy carrier in the transition to sustainable energy systems. Integrating dark fermentation (DF) and microbial electrolysis cells (MEC) offers an effective strategy to maximize hydrogen recovery from organic substrates. Herein, we investigated an integrated DF–MEC system operated using cheese whey (CW) as feedstock focusing on the development of anodic electro-active biofilm (EABf) acclimatization to improve continuous hydrogen production and process performance. EABf acclimatization strategy was initially developed in H-type cells using either acetate or a synthetic mixture designed to mimic the composition of DF effluents. Synthetic mixture acclimatization developed a highly diverse EABf that outperformed the acetate-acclimatized biofilms when real DF effluent was fed to H-type cells, both in terms of chemical oxygen demand (COD) removal efficiency (58±6 %) and Cathodic Capture Efficiency (98±2%). Based on these results, the graphite-packed anode (0.77L) of a continuous-flow MEC was first acclimated with the synthetic mixture (Run 1) and subsequently fed with CW-DF effluent (Run 2). In Run 2 the COD removal efficiency reached 88 ± 2%, showing a coulombic efficiency of 98 ± 4 % and a volumetric hydrogen production rate of 0.40 ± 0.01 L L⁻¹d⁻¹. Microbiological analysis revealed a functional active anodic biofilm, in which fermentative genera, such as Clostridium, Proteiniclatricum and Klebsiella, were particularly abundant (~40%), contributing to substrate conversion in syntrophy with genera, including Desulfitobacterium, Pseudomonas and Tissierella, associated with electrogenic activity (~20%). These findings demonstrate that acclimatization strategy promotes the establishment of specialized anodic consortia enhancing the overall performance of integrated DF–MEC systems.