Nitrogen (N) is an essential macronutrient for plant growth and development. To support agricultural production and enhance crop yield, two major N sources, nitrate and ammonium, are applied as fertilizers to the soil. Although many studies have been conducted on N uptake and signal transduction, the molecular genetic mechanisms of N-mediated physiological roles, such as the secondary growth of storage roots, remain largely unknown. One-year-old P. ginseng seedlings treated with KNO₃ were analyzed for the secondary growth of storage roots. The histological paraffin sections were subjected to bright and polarized light microscopic analysis. Genome-wide RNA-seq and network analysis were carried out to dissect the molecular mechanism of nitrate-mediated promotion of ginseng storage root thickening. Here, we report the positive effects of nitrate on storage root secondary growth in Panax ginseng. Exogenous nitrate supply to ginseng seedlings significantly increased the root secondary growth. Histological analysis indicated that the enhancement of root secondary growth could be attributed to the increase in cambium stem cell activity and the subsequent differentiation of cambium-derived storage parenchymal cells. RNA-seq and gene set enrichment analysis (GSEA) revealed that the formation of a transcriptional network comprising auxin, brassinosteroid (BR)-, ethylene-, and jasmonic acid (JA)-related genes mainly contributed to the secondary growth of ginseng storage roots. In addition, increased proliferation of cambium stem cells by a N-rich source inhibited the accumulation of starch granules in storage parenchymal cells. Thus, through the integration of bioinformatic and histological tissue analyses, we demonstrate that nitrate assimilation and signaling pathways are integrated into key biological processes that promote the secondary growth of P. ginseng storage roots.

High temperature is one of the most significant abiotic stresses reducing crop yield and quality by inhibiting plant growth and development. Global warming has recently increased the frequency of heat waves, which negatively impacts agricultural fields. Despite numerous studies on heat stress responses and signal transduction in model plant species, the molecular mechanism underlying thermomorphogenesis in Panax ginseng remains largely unknown. Here, we investigated the high temperature response of ginseng at the phenotypic and molecular levels. Both the primary shoot growth and secondary root growth of ginseng plants were significantly reduced at high temperature. Histological analysis revealed that these decreases in shoot and root growth were caused by decreases in cell elongation and cambium stem cell activity, respectively. Analysis of P. ginseng RNA-seq data revealed that heat-stress-repressed stem and root growth is closely related to changes in photosynthesis, cell wall organization, cell wall loosening, and abscisic acid (ABA) and jasmonic acid (JA) signaling. Reduction in both the light and dark reactions of photosynthesis resulted in defects in starch granule development in the storage parenchymal cells of the main tap root. Thus, by combining bioinformatics and histological analyses, we show that high temperature signaling pathways are integrated with crucial biological processes that repress stem and root growth in ginseng, providing novel insight into the heat stress response mechanism of P. ginseng.

Anthocyanins are generally accumulated within a few layers, including the epidermal cells of leaves and stems in plants. Solanum tuberosum cv. ‘Jayoung’ (hereafter, JY) is known to accumulate anthocyanin both in inner tissues and skins. We discovered that anthocyanin accumulation in the inner tissues of JY was almost diminished (more than 95% was decreased) in tuber induction condition. To investigate the transcriptomic mechanism of anthocyanin accumulation in JY flesh, which can be modulated by growth condition, we performed mRNA sequencing with white-colored flesh tissue of Solanum tuberosum cv. ‘Atlantic’ (hereafter, ‘Daeseo’, DS) grown under canonical growth conditions, a JY flesh sample grown under canonical growth conditions, and a JY flesh sample grown under tuber induction conditions. We could identify 36 common DEGs (differentially expressed genes) in JY flesh from canonical growth conditions that showed JY-specifically increased or decreased expression level. These genes were enriched with flavonoid biosynthetic process terms in GO analysis, as well as gene set enrichment analysis (GSEA) analysis. Further in silico analysis on expression levels of anthocyanin biosynthetic genes including rate-limiting genes such as StCHS and StCHI followed by RT-PCR and qRT-PCR analysis showed a strong positive correlation with the observed phenotypes. Finally, we identified StWRKY44 from 36 common DEGs as a possible regulator of anthocyanin accumulation, which was further supported by network analysis. In conclusion, we identified StWRKY44 as a putative regulator of tuber-induction-dependent anthocyanin accumulation.

Plant endophyte and epiphyte communities cooperatively interact with their host plants and play crucial roles in sustaining plant fitness. In Korea, a variety of studies have been conducted to elucidate the reasons for the declining population of the endangered Korean fir (Abies koreana), but the relationship between microbiota and the healthy condition of trees remains unclear. Here, we conducted bacterial 16S rRNA gene and fungal ITS sequence analyses to dissect the composition of endophytic and epiphytic microbiota in both live and dead trees located in the same Mt. Jiri habitat. In the live trees, the bacterial class Armatimonadia and the lichenized fungi groups were significantly dominant, whereas many bacterial and fungal taxa mainly found in rotten wood were enriched in the dead trees. Functional prediction of the microbial communities in live trees suggested the possibility that bacterial endophytes and epiphytes play a role in inorganic nutrient metabolism and fungal endophytes and epiphytes produce biologically active secondary metabolites, thereby contributing to the healthy condition of Korean fir trees. The ecological function of endophytes and epiphytes in dead trees was predicted to be involved in the decomposition of wood for nutrient recycling. Our analyses revealed a distinct difference in microbial communities depending on the health condition of Korean fir trees. The results from this study would be useful for understanding the ecological function of endophytic and epiphytic microorganisms to conserve and manage this endangered species from ecologically vulnerable environments.

Introduction: Ambient temperature-induced hypocotyl elongation in Arabidopsis seedlings is sensed by the epidermis-localized phytochrome B (phyB) and transduced into auxin biosynthesis via a basic helix-loop-helix transcription factor, phytochrome-interacting factor 4 (PIF4). Once synthesized, auxin travels down from the cotyledons to the hypocotyl, triggering hypocotyl cell elongation. Thus, the phyB-PIF4 module involved in thermosensing and signal transduction is a potential genetic target for engineering warm temperature-insensitive plants. Objectives: This study aims to manipulate warm temperature-induced elongation of plants at the post- translational level using phyB variants with dark reversion, the expression of which is subjected to heat stress. Methods: The thermosensitive growth response of Arabidopsis was manipulated by expressing the single amino acid substitution variant of phyB (phyB[G515E]), which exhibited a lower dark reversion rate than wild-type phyB. Other variants with slow (phyB[G564E]) or rapid (phyB[S584F]) dark reversion or light insensitivity (phyB[G767R]) were also included in this study for comparison. Warming-induced transient expression of phyB variants was achieved using heat shock-inducible promoters. Arabidopsis PHYB [G515E] and PHYB[G564E] were also constitutively expressed in rice in an attempt to manipulate the heat sensitivity of a monocotyledonous plant species. Results: At an elevated temperature, Arabidopsis seedlings transiently expressing PHYB[G515E] under the control of a heat shock-inducible promoter exhibited shorter hypocotyls than those expressing PHYB and other PHYB variant genes. This warm temperature-insensitive growth was related to the lowered PIF4 and auxin responses. In addition, transgenic rice seedlings expressing Arabidopsis PHYB[G515E] and PHYB[G564E] showed warm temperature-insensitive shoot growth. Conclusion: Transient expression of phyB variants with altered dark reversion rates could serve as an effective optogenetic technique for manipulating PIF4-auxin-mediated thermomorphogenic responses in plants. (c) 2024 The Authors. Published by Elsevier B.V. on behalf of Cairo University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).