Qiuying Pang

Key message HUB1 positively regulates salt tolerance in Arabidopsis by modulating H2Bub1 dynamic within the gene bodies of salt-responsive genes, thereby regulating their transcription reprogramming Abstract Soil salinity severely limits plant growth and agricultural productivity worldwide, driving plants to rely on rapid transcriptional reprogramming for stress adaptation. Histone H2B monoubiquitination (H2Bub1) is a conserved chromatin modification associated with active gene transcription. However, the role of H2Bub1 in response to salt stress remains unclear, and whether H2Bub1 occupancy work on the gene responsiveness upon salinity is obscure. Here, we demonstrate that HUB1 acts as a key positive regulator of salt tolerance. Loss of HUB1 results in pronounced salt hypersensitivity, characterized by excessive reactive oxygen species accumulation, disrupted Na⁺/K⁺ homeostasis, reduced osmolyte accumulation, and impaired growth under saline conditions, whereas overexpression HUB1 enhances salt tolerance. Transcriptome analyses reveal widespread misregulation of salt-responsive genes in hub1-7, accompanied by defects in metabolic processes, ABA- and MAPK-mediated signaling pathways. Genome-wide chromatin immunoprecipitation sequencing (ChIP-Seq) shows that salt stress induces a global redistribution of H2Bub1, with increased enrichment within gene bodies that positively correlates with transcriptional activation of salt-induced genes. Collectively, our findings establish HUB1-mediated H2Bub1 dynamics at gene bodies as an important chromatin-based mechanism for transcriptional regulation and salt stress adaptation in Arabidopsis, providing new insights into epigenetic control of plant stress responses.

Diatoms exhibit high competitive capacity in nitrogen assimilation, but the underlying mechanisms remain unclear. Here, we identify a non-ribosomal peptide synthase-like gene (PtNRPS1) with an atypical domain structure (A-T-R₁-R₂) in the marine diatom Phaeodactylum tricornutum, crucial for short-term nitrogen assimilation. In vitro enzyme assays show PtNRPS1 catalyzes conversion of L-tryptophan to tryptophanol, a tryptophan-derived indole compound that promotes diatom growth at concentrations far lower than indole-3-acetic acid. Transcriptomic, metabolomic analyses, and stable-isotope analyses indicate tryptophanol enhances short-term nitrogen assimilation. CRISPR-Cas9 knockout of PtNRPS1 abolishes tryptophanol biosynthesis and reduces nitrogen-assimilation enzymes activities, which are restored by exogenous tryptophanol. PtNRPS1 overexpression results in delayed but sustained enzyme elevation. Global distribution of PtNRPS1 homologues in stramenopiles positively correlates with nitrogen-assimilation gene abundance. Our findings suggest tryptophanol, synthesized by a diatom NRPS, accelerates nitrogen assimilation, providing a competitive edge in oceanic nitrogen acquisition.

Cytochrome P450 enzymes (CYPs) are crucial catalysts responsible for the oxidative modification of diverse substrates, including plant hormones, antioxidants, and compounds involved in abiotic stress responses. While CYP functions in drought and salt stress adaptation have been extensively studied, their contribution to alkaline stress tolerance, particularly concerning specific cytochrome P450 genes in wild soybean (Glycine soja), remains less explored. In this study, a cytochrome P450 gene, GsCYP93D1, was identified and isolated, and its regulatory role under alkaline stress was elucidated. Transgenic GsCYP93D1 increased Arabidopsis and soybean hairy root resistance to alkaline stress, but the Arabidopsis atcyp93d1 mutant showed a reduced capacity for alkaline tolerance. Subsequent investigation showed the enhanced antioxidant defense capabilities of GsCYP93D1 transgenic plants, as evidenced by reduced superoxide radical (O₂⁻) production under exposure to alkaline stress. Furthermore, compared to the atcyp93d1 mutant, transgenic lines of GsCYP93D1 showed sensitivity to ABA. Moreover, transcript levels of genes associated with alkaline stress response and ABA signaling pathways were elevated in both GsCYP93D1 transgenic and mutant lines. Collectively, our findings demonstrate that GsCYP93D1 positively modulates plant tolerance to alkaline stress and enhances ABA sensitivity.

Diatoms exhibit superior competitive capacity in nitrogen assimilation, largely contributing to their growth, although the mechanisms underpinning their success have not been completely understood. Here, a non-ribosomal peptide synthase-like (PtNRPS1, with an unusual domain structure A-T-R ₁ -R ₂ ) gene was found to play a vital role in short-term nitrogen assimilation in the marine diatom Phaeodactylum tricornutum . In vitro biochemical assays and in vivo overexpression confirmed that PtNRPS1 catalyzed two sequential two-electron reductions of L-tryptophan to tryptophanol. Tryptophanol exhibits high structural and functional similarities to indole-3-acetic acid (IAA), the most typical phytohormone auxin. Surprisingly, the effective concentration of tryptophanol was lower than that of IAA by as much as 2-5 orders of magnitude for P. tricornutum . Compared with the action of IAA, a distinct molecular mode for tryptophanol was revealed by transcriptomic analysis, resulting mainly in enhanced short-term nitrogen assimilation, which was also confirmed by the elevated nitrogen uptake rates determined by stable-isotope tracking. Finally, global distribution of PtNRPS1 homologues from stramenopiles was found to be positively correlated with the abundance of genes involved in nitrogen assimilation pathways. Overall, our study provides evidence of an auxin-like derivative synthesized by an NRPS in a diatom. We speculate that tryptophanol may accelerate nitrogen assimilation, conferring advantages in the competition for nitrogen in the ocean.

Alfalfa (Medicago sativa) is a perennial forage crop with significant economic and ecological significance. If alfalfa can be planted in saline-alkali land, it will not only improve the utilization rate of marginal land and alleviate the competition between forage and cereal crops for arable land but will also increase the yield of high-quality domestic forage. In this study, we conducted transcriptomic analysis on the saline-alkali-tolerant alfalfa cultivar NQ-1 and compared its metabolite accumulation levels with saline-alkali-sensitive cultivars. The results showed that under saline-alkali stress, the photosynthesis and some secondary metabolic pathways in NQ-1 were activated, such as α-Linolenic acid metabolism, Phenylpropanoid and Flavonoid biosynthesis, and Photosynthesis-related pathways, providing substances and energy for enhancing NQ-1 stress tolerance. Furthermore, some specific flavonoids were detected that may contribute to the saline-alkali tolerance of NQ-1. In addition, transcription factors that may regulate flavonoid biosynthesis in NQ-1 under saline-alkali stress were also identified. This study deepens the understanding of the resistance mechanism of saline-alkali-tolerant cultivars of alfalfa and provides valuable information for molecular design breeding strategies for stress-resistant alfalfa.

Plant growth‐promoting rhizobacteria (PGPR) are known for their role in ameliorating plant stress, including alkaline stress, yet the mechanisms involved are not fully understood. This study investigates the impact of various inoculum doses of Bacillus licheniformis Jrh14‐10 on Arabidopsis growth under alkaline stress and explores the underlying mechanisms of tolerance enhancement. We found that all tested doses improved the growth of NaHCO₃‐treated seedlings, with 10⁹ cfu/mL being the most effective. Transcriptome analysis indicated downregulation of ethylene‐related genes and an upregulation of polyamine biosynthesis genes following Jrh14‐10 treatment under alkaline conditions. Further qRT‐PCR analysis confirmed the suppression of ethylene biosynthesis and signaling genes, alongside the activation of polyamine biosynthesis genes in NaHCO₃‐stressed seedlings treated with Jrh14‐10. Genetic analysis showed that ethylene signaling‐deficient mutants (etr1‐3 and ein3‐1) exhibited greater tolerance to NaHCO₃ than the wild type, and the growth‐promoting effect of Jrh14‐10 was significantly diminished in these mutants. Additionally, Jrh14‐10 was found unable to produce 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase, indicating it does not reduce the ethylene precursor ACC in Arabidopsis. However, Jrh14‐10 treatment increased the levels of polyamines (putrescine, spermidine, and spermine) in stressed seedlings, with spermidine particularly effective in reducing H₂O₂ levels and enhancing F_v/F_m under NaHCO₃ stress. These findings reveal a novel mechanism of PGPR‐induced alkaline tolerance, highlighting the crosstalk between ethylene and polyamine pathways, and suggest a strategic redirection of S‐adenosylmethionine towards polyamine biosynthesis to combat alkaline stress.