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Li X, Yell V, Li X. Two Arabidopsis promoters drive seed-coat specific gene expression in pennycress and camelina. PLANT METHODS 2023; 19:140. [PMID: 38053155 DOI: 10.1186/s13007-023-01114-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 11/20/2023] [Indexed: 12/07/2023]
Abstract
BACKGROUND Pennycress and camelina are two important novel biofuel oilseed crop species. Their seeds contain high content of oil that can be easily converted into biodiesel or jet fuel, while the left-over materials are usually made into press cake meals for feeding livestock. Therefore, the ability to manipulate the seed coat encapsulating the oil- and protein-rich embryos is critical for improving seed oil production and press cake quality. RESULTS Here, we tested the promoter activity of two Arabidopsis seed coat genes, AtTT10 and AtDP1, in pennycress and camelina by using eGFP and GUS reporters. Overall, both promoters show high levels of activities in the seed coat in these two biofuel crops, with very low or no expression in other tissues. Importantly, AtTT10 promoter activity in camelina shows differences from that in Arabidopsis, which highlights that the behavior of an exogenous promoter in closely related species cannot be assumed the same and still requires experimental determination. CONCLUSION Our work demonstrates that AtTT10 and AtDP1 promoters are suitable for driving gene expression in the outer integument of the seed coat in pennycress and camelina.
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Affiliation(s)
- Xin Li
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695, USA
- Plants for Human Health Institute, North Carolina State University, Kannapolis, NC, 28081, USA
| | - Victoria Yell
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695, USA
- Plants for Human Health Institute, North Carolina State University, Kannapolis, NC, 28081, USA
| | - Xu Li
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695, USA.
- Plants for Human Health Institute, North Carolina State University, Kannapolis, NC, 28081, USA.
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Allen PJ, Napoli RS, Parish RW, Li SF. MYB-bHLH-TTG1 in a Multi-tiered Pathway Regulates Arabidopsis Seed Coat Mucilage Biosynthesis Genes Including PECTIN METHYLESTERASE INHIBITOR14 Required for Homogalacturonan Demethylesterification. PLANT & CELL PHYSIOLOGY 2023; 64:906-919. [PMID: 37354456 PMCID: PMC10434736 DOI: 10.1093/pcp/pcad065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 05/16/2023] [Accepted: 06/23/2023] [Indexed: 06/26/2023]
Abstract
MYB-bHLH-TTG1 (MBW) transcription factor (TF) complexes regulate Arabidopsis seed coat biosynthesis pathways via a multi-tiered regulatory mechanism. The MYB genes include MYB5, MYB23 and TRANSPARENT TESTA2 (TT2), which regulate GLABRA2 (GL2), HOMEODOMAIN GLABROUS2 (HDG2) and TRANSPARENT TESTA GLABRA2 (TTG2). Here, we examine the role of PECTIN METHYLESTERASE INHIBITOR14 (PMEI14) in seed coat mucilage pectin methylesterification and provide evidence in support of multi-tiered regulation of seed coat mucilage biosynthesis genes including PMEI14. The PMEI14 promoter was active in the seed coat and developing embryo. A pmei14 mutant exhibited stronger attachment of the outer layer of seed coat mucilage, increased mucilage homogalacturonan demethylesterification and reduced seed coat radial cell wall thickness, results consistent with decreased PMEI activity giving rise to increased PME activity. Reduced mucilage release from the seeds of myb5, myb23, tt2 and gl2, hdg2, ttg2 triple mutants indicated that HDG2 and MYB23 play minor roles in seed coat mucilage deposition. Chromatin immunoprecipitation analysis found that MYB5, TT8 and seven mucilage pathway structural genes are directly regulated by MYB5. Expression levels of GL2, HDG2, TTG2 and nine mucilage biosynthesis genes including PMEI14 in the combinatorial mutant seeds indicated that these genes are positively regulated by at least two of those six TFs and that TTG1 and TTG2 are major regulators of PMEI14 expression. Our results show that MYB-bHLH-TTG1 complexes regulate mucilage biosynthesis genes, including PMEI14, both directly and indirectly via a three-tiered mechanism involving GL2, HDG2 and TTG2.
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Affiliation(s)
- Patrick J Allen
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Melbourne, Victoria 3086, Australia
| | - Ross S Napoli
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Melbourne, Victoria 3086, Australia
| | - Roger W Parish
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Melbourne, Victoria 3086, Australia
| | - Song Feng Li
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Melbourne, Victoria 3086, Australia
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McGee R, Dean GH, Wu D, Zhang Y, Mansfield SD, Haughn GW. Pectin Modification in Seed Coat Mucilage by In Vivo Expression of Rhamnogalacturonan-I- and Homogalacturonan-Degrading Enzymes. PLANT & CELL PHYSIOLOGY 2021; 62:1912-1926. [PMID: 34059917 DOI: 10.1093/pcp/pcab077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Revised: 04/23/2021] [Accepted: 05/31/2021] [Indexed: 05/27/2023]
Abstract
The cell wall is essential for plant survival. Determining the relationship between cell wall structure and function using mutant analysis or overexpressing cell wall-modifying enzymes has been challenging due to the complexity of the cell wall and the appearance of secondary, compensatory effects when individual polymers are modified. In addition, viability of the plants can be severely impacted by wall modification. A useful model system for studying structure-function relationships among extracellular matrix components is the seed coat epidermal cells of Arabidopsis thaliana. These cells synthesize relatively simple, easily accessible, pectin-rich mucilage that is not essential for plant viability. In this study, we expressed enzymes predicted to modify polysaccharide components of mucilage in the apoplast of seed coat epidermal cells and explored their impacts on mucilage. The seed coat epidermal-specific promoter TESTA ABUNDANT2 (TBA2) was used to drive expression of these enzymes to avoid adverse effects in other parts of the plant. Mature transgenic seeds expressing Rhamnogalacturonate lyase A (RglA) or Rhamnogalacturonate lyase B (RglB) that degrade the pectin rhamnogalacturonan-I (RG-I), a major component of mucilage, had greatly reduced mucilage capsules surrounding the seeds and concomitant decreases in the monosaccharides that comprise the RG-I backbone. Degradation of the minor mucilage component homogalacturonan (HG) using the HG-degrading enzymes Pectin lyase A (PLA) or ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE2 (ADPG2) resulted in developing seed coat epidermal cells with disrupted cell-cell adhesion and signs of early cell death. These results demonstrate the feasibility of manipulating the seed coat epidermal cell extracellular matrix using a targeted genetic engineering approach.
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Affiliation(s)
- Robert McGee
- Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
- L'Institut National de la Recherche Scientifique Centre Armand-Frappier Santé Biotechnologie (INRS-CAFSB), 531 des Prairies Blvd. Laval, QC, H7V 1B7, Canada
| | - Gillian H Dean
- Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
| | - Di Wu
- Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
- Faculty of Land and Food Systems, University of British Columbia, 248-2357 Main Mall Vancouver, BC V6T 1Z4, Canada
| | - Yuelin Zhang
- Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
| | - Shawn D Mansfield
- Department of Wood Science, University of British Columbia, 2900-2424 Main Mall Vancouver, BC V6T 1Z4, Canada
| | - George W Haughn
- Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
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Tsai AYL, McGee R, Dean GH, Haughn GW, Sawa S. Seed Mucilage: Biological Functions and Potential Applications in Biotechnology. PLANT & CELL PHYSIOLOGY 2021; 62:1847-1857. [PMID: 34195842 DOI: 10.1093/pcp/pcab099] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Revised: 05/16/2021] [Accepted: 06/30/2021] [Indexed: 06/13/2023]
Abstract
In plants, the diaspore (seed dispersal unit) may include a seed coat and/or pericarp to protect the embryo and assist in dispersion. In many species, the seed coat and/or pericarp secrete a gelatinous mixture of cell wall polysaccharides known as mucilage. In several species, mucilage synthesis, secretion and modification have been studied extensively as model systems for the investigation of plant cell wall structure and function. Despite this, efforts toward understanding the role of mucilage have received less attention. Mucilage has been hypothesized to impact seed dispersal through interaction with soil, protecting the seed in the gut following ingestion by animals or affecting the ability of seeds to sink or float in water. Mucilage has been found to influence seed germination and seedling establishment, most often during abiotic stress, probably by maintaining seed hydration when water is scarce. Finally, mucilage has been documented to mediate interactions with various organisms. Advances in transgenic technology should enable the genetic modification of mucilage structure and function in crop plants. Cells synthesizing mucilage may also be a suitable platform for creating custom polysaccharides or proteins with industrial applications. Thus, in the near future, it is likely that research on seed mucilage will expand well beyond the current focus. Here we summarize our understanding of the biological functions of mucilage and provide an outlook on the future of mucilage research.
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Affiliation(s)
- Allen Yi-Lun Tsai
- International Research Center for Agricultural & Environmental Biology, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo Ward, Kumamoto 860-8555, Japan
| | - Robert McGee
- L'Institut National de la Recherche Scientifique Centre Armand-Frappier Santé Biotechnologie (INRS-CAFSB), 531 des Prairies Blvd, Laval, QC H7V 1B7, Canada
| | - Gillian H Dean
- Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
| | - George W Haughn
- Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
| | - Shinichiro Sawa
- International Research Center for Agricultural & Environmental Biology, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo Ward, Kumamoto 860-8555, Japan
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Lee Y, Dean GH, Gilchrist E, Tsai AY, Haughn GW. Asymmetric distribution of extracellular matrix proteins in seed coat epidermal cells of Arabidopsis is determined by polar secretion. PLANT DIRECT 2021; 5:e360. [PMID: 34877448 PMCID: PMC8628086 DOI: 10.1002/pld3.360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 10/18/2021] [Accepted: 10/21/2021] [Indexed: 06/13/2023]
Abstract
Although asymmetric deposition of the plant extracellular matrix is critical for the normal functioning of many cell types, the molecular mechanisms establishing this asymmetry are not well understood. During differentiation, Arabidopsis seed coat epidermal cells deposit large amounts of pectin-rich mucilage asymmetrically to form an extracellular pocket between the plasma membrane and the outer tangential primary cell wall. At maturity, the mucilage expands on contact with water, ruptures the primary cell wall, and extrudes to encapsulate the seed. In addition to polysaccharides, mucilage contains secreted proteins including the β-galactosidase MUCILAGE MODIFIED 2 (MUM2). A functional chimeric protein where MUM2 was fused translationally with Citrine yellow fluorescent protein (Citrine) indicated that MUM2-Citrine fluorescence preferentially accumulates in the mucilage pocket concomitant with mucilage deposition and rapidly disappears when mucilage synthesis ceases. A secreted form of Citrine, secCitrine, showed a similar pattern of localization when expressed in developing seed coat epidermal cells. This result suggested that both the asymmetric localization and rapid decrease of fluorescence is not unique to MUM2-Citrine and may represent the default pathway for secreted proteins in this cell type. v-SNARE proteins were localized only in the membrane adjacent to the mucilage pocket, supporting the hypothesis that the cellular secretory apparatus is redirected and targets secretion to the outer periclinal apoplast during mucilage synthesis. In addition, mutation of ECHIDNA, a gene encoding a TGN-localized protein involved in vesicle targeting, causes misdirection of mucilage, MUM2 and v-SNARE proteins from the apoplast/plasma membrane to the vacuole/tonoplast. Western blot analyses suggested that the disappearance of MUM2-Citrine fluorescence at the end of mucilage synthesis is due to protein degradation and because several proteases have been identified in extruded seed mucilage. However, as mutation of these genes did not result in a substantial delay in MUM2-Citrine degradation and the timing of their expression and/or their intracellular localization were not consistent with a role in MUM2-Citrine disappearance, the mechanism underlying the abrupt decrease of MUM2-Citrine remains unclear.
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Affiliation(s)
- Yi‐Chen Lee
- Department of BotanyUniversity of British ColumbiaVancouverCanada
- Present address:
Biodiversity Research CenterAcademia SinicaTaipeiTaiwan
| | - Gillian H. Dean
- Department of BotanyUniversity of British ColumbiaVancouverCanada
| | - Erin Gilchrist
- Department of BotanyUniversity of British ColumbiaVancouverCanada
- Present address:
Molecular DiagnosticsAnandia LaboratoriesVancouverCanada
| | - Allen Yi‐Lun Tsai
- Department of BotanyUniversity of British ColumbiaVancouverCanada
- Present address:
International Research Center for Agricultural & Environmental Biology, Faculty of Advanced Science and TechnologyKumamoto UniversityKumamotoJapan
| | - George W. Haughn
- Department of BotanyUniversity of British ColumbiaVancouverCanada
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McGee R, Dean GH, Mansfield SD, Haughn GW. Assessing the utility of seed coat-specific promoters to engineer cell wall polysaccharide composition of mucilage. PLANT MOLECULAR BIOLOGY 2019; 101:373-387. [PMID: 31422517 DOI: 10.1007/s11103-019-00909-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 08/09/2019] [Indexed: 06/10/2023]
Abstract
Polysaccharide composition of seed mucilage was successfully modified using three seed coat-specific promoters driving expression of genes encoding cell wall-modifying enzymes. Arabidopsis thaliana seed coat epidermal cells synthesize and secrete large quantities of mucilage, a specialized secondary cell wall composed of cellulose, hemicellulose, and pectin. The composition and structure of mucilage confers its unique properties of expansion, extrusion, and adherence. We are developing seed mucilage as a model to study the biochemical and biological consequences of manipulating cell wall polysaccharides in vivo using cell wall-modifying enzymes. To specifically engineer mucilage composition and avoid altering other cell types, seed coat-specific promoters are required. In this study, we investigated the ability of seed coat-specific promoters from three genes, TESTA-ABUNDANT2 (TBA2), PEROXIDASE36 (PER36), and MUCILAGE-MODIFIED4 (MUM4), to express the cell wall modifying β-galactosidase (BGAL)-encoding gene MUCILAGE-MODIFIED2 (MUM2) and complement the mum2 mutant. The strength of the three promoters relative to one another was found to vary by two to 250 fold, and correlated with their ability to rescue the mum2 mutant phenotype. The strongest of the three promoters, TBA2p, was then used to examine the ability of three MUM2 homologs to complement the mum2 extrusion and cell wall composition phenotypes. The degree of complementation was variable and correlated with the amino acid sequence similarity between the homologous gene products and MUM2. These data demonstrate that all three seed coat-specific promoters can drive expression of genes encoding carbohydrate-active enzymes in a spatial and temporal pattern sufficiently to modify polysaccharide composition in seed mucilage without obvious negative consequences to the rest of the plant.
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Affiliation(s)
- Robert McGee
- Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada
| | - Gillian H Dean
- Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada
| | - Shawn D Mansfield
- Department of Wood Science, University of British Columbia, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
| | - George W Haughn
- Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada.
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Francoz E, Lepiniec L, North HM. Seed coats as an alternative molecular factory: thinking outside the box. PLANT REPRODUCTION 2018; 31:327-342. [PMID: 30056618 DOI: 10.1007/s00497-018-0345-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 07/13/2018] [Indexed: 05/15/2023]
Abstract
Seed coats as commodities. Seed coats play important roles in the protection of the embryo from biological attack and physical damage by the environment as well as dispersion strategies. A significant part of the energy devoted by the mother plant to seed production is channeled into the production of the cell layers and metabolites that surround the embryo. Nevertheless, in crop species these are often discarded post-harvest and are a wasted resource that could be processed to yield co-products. The production of novel compounds from existing metabolites is also a possibility. A number of macromolecules are already accumulated in these maternal layers that could be exploited in industrial applications either directly or via green chemistry, notably flavonoids, lignin, lignan, polysaccharides, lipid polyesters and waxes. Here, we summarize our knowledge of the in planta biosynthesis pathways of these macromolecules and their molecular regulation as well as potential applications. We also outline recent work aimed at providing further tools for increasing yields of existing molecules or the development of novel biotech approaches, as well as trial studies aimed at exploiting this underused resource.
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Affiliation(s)
- Edith Francoz
- Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, 78000, Versailles, France
| | - Loïc Lepiniec
- Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, 78000, Versailles, France
| | - Helen M North
- Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, 78000, Versailles, France.
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Golz JF, Allen PJ, Li SF, Parish RW, Jayawardana NU, Bacic A, Doblin MS. Layers of regulation - Insights into the role of transcription factors controlling mucilage production in the Arabidopsis seed coat. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 272:179-192. [PMID: 29807590 DOI: 10.1016/j.plantsci.2018.04.021] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2018] [Revised: 04/22/2018] [Accepted: 04/24/2018] [Indexed: 05/12/2023]
Abstract
A polysaccharide-rich mucilage is released from the seed coat epidermis of numerous plant species and has been intensively studied in the model plant Arabidopsis. This has led to the identification of a large number of genes involved in the synthesis, secretion and modification of cell wall polysaccharides such as pectin, hemicellulose and cellulose being identified. These genes include a small network of transcription factors (TFs) and transcriptional co-regulators, that not only regulate mucilage production, but epidermal cell differentiation and in some cases flavonoid biosynthesis in the internal endothelial layer of the seed coat. Here we focus on the function of these regulators and propose a simplified model where they are assigned to a hierarchical gene network with three regulatory levels (tiers) as a means of assisting in the interpretation of the complexity. We discuss limitations of current methodologies and highlight some of the problems associated with defining the function of TFs, particularly those that perform different functions in adjacent layers of the seed coat. We suggest approaches that should provide a more accurate picture of the function of transcription factors involved with mucilage production and release.
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Affiliation(s)
- John F Golz
- School of BioSciences, University of Melbourne, Royal Parade, Parkville, VIC 3010, Australia.
| | - Patrick J Allen
- Department of Animal, Plant and Soil Sciences, AgriBio Centre, School of Life Sciences, La Trobe University, Bundoora, VIC 3086, Australia
| | - Song F Li
- Department of Animal, Plant and Soil Sciences, AgriBio Centre, School of Life Sciences, La Trobe University, Bundoora, VIC 3086, Australia
| | - Roger W Parish
- Department of Animal, Plant and Soil Sciences, AgriBio Centre, School of Life Sciences, La Trobe University, Bundoora, VIC 3086, Australia
| | - Nadeeka U Jayawardana
- ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Antony Bacic
- ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Monika S Doblin
- ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Parkville, VIC 3010, Australia
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