title: The OCL3 promoter from Sorghum bicolor directs gene expression to abscission and nutrient-transfer zones at the bases of floral organs.
abstract: OBJECTIVE
  During seed fill in cereals, nutrients are symplasmically unloaded to vascular parenchyma in ovules, but thereafter nutrient transport is less certain. In Zea mays, two mechanisms of nutrient passage through the chalaza and nucellus have been hypothesized, apoplasmic and symplasmic. In a recent study, nutrients first passed non-selectively to the chalazal apoplasm and were then selectively absorbed by the nucellus before being released to the endosperm apoplasm. This study reports that the promoter of OUTER CELL LAYER3 (PSbOCL3) from Sorghum bicolor (sorghum) directs gene expression to chalazal cells where the apoplasmic barrier is thought to form. The aims were to elucidate PSbOCL3 expression patterns in sorghum and relate them to processes of nutrient pathway development in kernels and to recognized functions of the homeodomain-leucine zipper (HD-Zip) IV transcription factor family to which the promoter belongs.
  
  
  METHODS
  PSbOCL3 was cloned and transformed into sorghum as a promoter-GUS (β-glucuronidase) construct. Plant tissues from control and transformed plants were then stained for GUS, and kernels were cleared and characterized using differential interference contrast microscopy.
  
  
  RESULTS
  A symplasmic disconnect between the chalaza and nucellus during seed fill is inferred by the combination of two phenomena: differentiation of a distinct nucellar epidermis adjacent to the chalaza, and lysis of GUS-stained chalazal cells immediately proximal to the nucellar epidermis. Compression of the GUS-stained chalazal cells during kernel maturation produced the kernel abscission zone (closing layer).
  
  
  CONCLUSIONS
  The results suggest that the HD-Zip IV transcription factor SbOCL3 regulates kernel nutrition and abscission. The latter is consistent with evidence that members of this transcription factor group regulate silique abscission and dehiscence in Arabidopsis thaliana. Collectively, the findings suggest that processes of floral organ abscission are conserved among angiosperms and may in some respects differ from processes of leaf abscission.
authors: Caisson Laboratories, Inc., 1740 Research Park Way, North Logan, UT 84341, USA Crop Improvement Division, Indian Grassland and Fodder Research Institute, Jhansi (UP) 284003, India Plants, Soils and Climate Department, Utah State University, Logan, UT 84322-4820, USA.
authors: Krishna K
authors: KK
authors: Dwivedi
authors: Caisson Laboratories, Inc., 1740 Research Park Way, North Logan, UT 84341, USA PhytoGen Seed Co. LLC, Western Research Station, 850 Plymouth Avenue, Corcoran, CA 93212, USA.
authors: Dominique J
authors: DJ
authors: Roche
authors: Department of Agronomy and Horticulture, Center for Plant Science Innovation, University of Nebraska, Lincoln, NE 68588, USA.
authors: Tom E
authors: TE
authors: Clemente
authors: Department of Agronomy and Horticulture, Center for Plant Science Innovation, University of Nebraska, Lincoln, NE 68588, USA.
authors: Zhengxiang
authors: Z
authors: Ge
authors: Caisson Laboratories, Inc., 1740 Research Park Way, North Logan, UT 84341, USA Plants, Soils and Climate Department, Utah State University, Logan, UT 84322-4820, USA john.carman@usu.edu.
authors: John G
authors: JG
authors: Carman
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D017385:Sequence Homology; D045868:Sorghum / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism
chemical_list: D010940:Plant Proteins
keywords: Abscission zone; OCL3; Sorghum bicolor; apoplast; closing layer; epidermis-specific; fruit abscission; kernel development; nutrient transport; promoter; seed fill; symplast