SCFFBS1 Regulates Root Quiescent Center Cell Division via Protein Degradation of APC/CCCS52A2

Kyoung Rok Geem,Hyemin Kim,Hojin Ryu 한국분자세포생물학회 2022 Molecules and cells Vol.45 No.10

Homeostatic regulation of meristematic stem cells accomplished by maintaining a balance between stem cell self-renewal and differentiation is critical for proper plant growth and development. The quiescent center (QC) regulates root apical meristem homeostasis by maintaining stem cell fate during plant root development. Cell cycle checkpoints, such as anaphase promoting complex/cyclosome/CELL CYCLE SWITCH 52 A2 (APC/CCCS52A2), strictly control the low proliferation rate of QC cells. Although APC/CCCS52A2 plays a critical role in maintaining QC cell division, the molecular mechanism that regulates its activity remains largely unknown. Here, we identified SCFF-BOX STRESS INDUCED 1 (FBS1), a ubiquitin E3 ligase, as a key regulator of QC cell division through the direct proteolysis of CCS52A2. FBS1 activity is positively associated with QC cell division and CCS52A2 proteolysis. FBS1 overexpression or ccs52a2-1 knockout consistently resulted in abnormal root development, characterized by root growth inhibition and low mitotic activity in the meristematic zone. Loss-of-function mutation of FBS1, on the other hand, resulted in low QC cell division, extremely low WOX5 expression, and rapid root growth. The 26S proteasome-mediated degradation of CCS52A2 was facilitated by its direct interaction with F-box stress induced 1 (FBS1). The FBS1 genetically interacted with APC/CCCS52A2-ERF115-PSKR1 signaling module for QC division. Thus, our findings establish SCFFBS1-mediated CCS52A2 proteolysis as the molecular mechanism for controlling QC cell division in plants.

Nitrate enhances the secondary growth of storage roots in Panax ginseng

Kyoung Rok Geem,Jaewook Kim,Wonsil Bae,Moo-Geun Jee,Jin Yu,Inbae Jang,Dong-Yun Lee,Chang Pyo Hong,Donghwan Shim,Hojin Ryu The Korean Society of Ginseng 2023 Journal of Ginseng Research Vol.47 No.3

Background: 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. Methods: 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. Results: 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. Conclusion: 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.

Cytokinin signaling promotes root secondary growth and bud formation in Panax ginseng

Kyoung Rok Geem,Yookyung Lim,Jeongeui Hong,Wonsil Bae,Jinsu Lee,Soeun Han,Jinsu Gil,Hyunwoo Cho,Hojin Ryu The Korean Society of Ginseng 2024 Journal of Ginseng Research Vol.48 No.2

Background: Panax ginseng, one of the valuable perennial medicinal plants, stores numerous pharmacological substrates in its storage roots. Given its perennial growth habit, organ regeneration occurs each year, and cambium stem cell activity is necessary for secondary growth and storage root formation. Cytokinin (CK) is a phytohormone involved in the maintenance of meristematic cells for the development of storage organs; however, its physiological role in storage-root secondary growth remains unknown. Methods: Exogenous CK was repeatedly applied to P. ginseng, and morphological and histological changes were observed. RNA-seq analysis was used to elucidate the transcriptional network of CK that regulates P. ginseng growth and development. The HISTIDINE KINASE 3 (PgHK3) and RESPONSE REGULATOR 2 (PgRR2) genes were cloned in P. ginseng and functionally analyzed in Arabidopsis as a two-component system involved in CK signaling. Results: Phenotypic and histological analyses showed that CK increased cambium activity and dormant axillary bud formation in P. ginseng, thus promoting storage-root secondary growth and bud formation. The evolutionarily conserved two-component signaling pathways in P. ginseng were sufficient to restore CK signaling in the Arabidopsis ahk2/3 double mutant and rescue its growth defects. Finally, RNA-seq analysis of CK-treated P. ginseng roots revealed that plant-type cell wall biogenesis-related genes are tightly connected with mitotic cell division, cytokinesis, and auxin signaling to regulate CK-mediated P. ginseng development. Conclusion: Overall, we identified the CK signaling-related two-component systems and their physiological role in P. ginseng. This scientific information has the potential to significantly improve the field-cultivation and biotechnology-based breeding of ginseng.

Sequence Motifs in Transit Peptides Act as Independent Functional Units and Can Be Transferred to New Sequence Contexts

Lee, Dong Wook,Woo, Seungjin,Geem, Kyoung Rok,Hwang, Inhwan American Society of Plant Biologists 2015 Plant Physiology Vol.169 No.1

<P><I>Various sequence motifs in diverse transit peptides act as independent functional units and can be transferred to new sequence contexts with the possibility of a change in their functionality.</I></P><P>A large number of nuclear-encoded proteins are imported into chloroplasts after they are translated in the cytosol. Import is mediated by transit peptides (TPs) at the N termini of these proteins. TPs contain many small motifs, each of which is critical for a specific step in the process of chloroplast protein import; however, it remains unknown how these motifs are organized to give rise to TPs with diverse sequences. In this study, we generated various hybrid TPs by swapping domains between Rubisco small subunit (RbcS) and chlorophyll <I>a/b</I>-binding protein, which have highly divergent sequences, and examined the abilities of the resultant TPs to deliver proteins into chloroplasts. Subsequently, we compared the functionality of sequence motifs in the hybrid TPs with those of wild-type TPs. The sequence motifs in the hybrid TPs exhibited three different modes of functionality, depending on their domain composition, as follows: active in both wild-type and hybrid TPs, active in wild-type TPs but inactive in hybrid TPs, and inactive in wild-type TPs but active in hybrid TPs. Moreover, synthetic TPs, in which only three critical motifs from RbcS or chlorophyll <I>a/b</I>-binding protein TPs were incorporated into an unrelated sequence, were able to deliver clients to chloroplasts with a comparable efficiency to RbcS TP. Based on these results, we propose that diverse sequence motifs in TPs are independent functional units that interact with specific translocon components at various steps during protein import and can be transferred to new sequence contexts.</P>