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Xcl1 causes delayed oblique periclinal cell divisions in developing maize leaves, leading to cellular differentiation by lineage instead of position

Sharon Kessler, Sumer Seiki and Neelima Sinha*

Section of Plant Biology, University of California, Davis, CA 95616, USA



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  		Fig. 1. Effects of Xcl1 on leaf morphology. (A) Wild-type seedling. (B) Xcl1 seedling has narrow, thick leaves that are shiny in appearance. Scale bars 2 cm. (C-E) Morphometric analysis of adult leaves (numbered from top of plant down) in the Tama Flint (Blue), W23 (Red) and B73 (green) backgrounds. Wild-type values are solid bars and Xcl1 values are hatched. (C) In all backgrounds, Xcl1 leaves are significantly shorter than wild-type leaves. (D) At the midpoint of the leaf blade, Xcl1 leaves are half as wide as wild-type leaves. (E) At the midpoint of the leaf blade, Xcl1 leaves are twice as thick as wild type. Similar width and thickness effects were seen at 1/4 and 3/4 the length of the blade.

 


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  		Fig. 2. Effects of Xcl1 on leaf anatomy. (A) Transverse section of a wild-type adult leaf. (B) Transverse section of Xcl1 leaf with large, thin walled cells beneath both the adaxial and abaxial epidermis. (C,E) Replica images of adaxial (C) and abaxial (E) epidermis of a wild-type leaf showing the regular placement of stomatal complexes (arrows) and crenulated pavement cell walls. (D,F) Xcl1 adaxial (D) and abaxial (F) epidermis with reduced stomatal complexes and crenulation of pavement cell walls. Scale bars, 100 µm.

 


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  		Fig. 3. Xcl1 effects on other parts of the maize plant. (A) KN1 immunolocalization on a median longitudinal section of a wild-type meristem showing down-regulation in the P0 and developing leaves. (B) KN1 expression in the Xcl1 meristem is normal, but the apical dome is significantly shorter. (C,D) Transverse sections through the root hair zone of wild-type (C) and Xcl1 (D) roots. The roots have similar numbers of cell layers (*indicates root cap cells). (E) SEM of wild-type kernel with pericarp removed showing one layer of aleurone cells (al) bordering the starchy endosperm (en). (F) Xcl1 kernel has 2 layers of aleurone cells. Scale bars A-B, 100 µm; C-D 500 µm; E-F, 25 µm.

 


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  		Fig. 4. The extra cells in the Xcl1 mutant have epidermal identity. (A-F) Immunolocalizations with cell-type-specific antibodies. Silver enhancement of the gold-conjugated secondary antibody produced a black signal. (A,B) The small subunit of RuBisCO is localized to the bundle sheath cells in both wild-type (A) and Xcl1 (B) leaves, but is not detected in the extra cell layer. (C,D) PEPC is localized to the mesophyll cells in wild-type (C) and Xcl1 (D) leaves, but is not in the extra cell layer. (E-F) ß (1,3) and (1,4) mixed linkage glucans are localized to epidermal and vascular cell walls in wild-type leaves (E) and in the extra cell layers in the Xcl1 mutant (F). (G) Anthocyanin production is limited to the epidermis in the adult wild-type leaf. (H) Anthocyanins are produced in both the epidermis and the extra cell layers in Xcl1. (I-J) ZmOCL5 is expressed in the outer cell layer in both wild-type (I) and Xcl1 (J) meristems and leaves. Scale bars A-J, 100 µm.

 


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  		Fig. 5. Clonal analysis for determining the origin of the extra cells. (A) Experimental design. (B) Wild-type sheath, expressing anthocyanins. (C) Xcl1 sheath has extra cell layers (asterisk) between the minor veins and the adaxial epidermis. (D) Non-informative sector extends through the epidermis and internal cell layers. (E) Sector with colored epidermis and extra cells and colorless internal cells. (F) Colorless sector extending through epidermis and the extra cell layers. Scale bars B-F, 100 µm.

 


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  		Fig. 6. Cell division patterns in developing leaf primordia. (A,E) Transverse sections through seedling meristems (M) including plastochrons (P) 1-3. (A) The wild-type leaves have 5 cell layer margins at P2 and P3 (asterisk). (E) Xcl1 P2 and P3 margins have disorganized cell layers and are thicker than normal. (B-D) Serial sections through a wild-type P4 margin with protoderm divisions (arrowhead) in the anticlinal plane and vascular bundles (V) near margin. (F-G) Serial sections through an Xcl1 P4 margin showing oblique periclinal divisions (arrows) in the protoderm and normal anticlinal divisions (arrowheads). Scale bars A, E, 100 µm; B-D and F-H, 25 µm.

 


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  		Fig. 7. Dosage analysis of Xcl1. (A) Large, colored kernel with hyperploid endosperm and hypoploid embryo. (B) Small, yellow kernel with hypoploid endosperm and hyperploid embryo with a colored scutellum (arrow). (C) TB-10L kernel hypoploid for xcl1 has one layer of aleurone. (D) TB-10L kernel hyperploid for xcl1 has regions with more than one layer of aleurone. (E-I) Free-hand transverse sections of leaves. (E) The hypoploid (Xcl1/0) leaf is thinner than wild-type and has no extra cell layers beneath the epidermis. (F) A wild-type (xcl1/xcl1) leaf. (G) Diploid (Xcl1/xcl1) leaf has infrequent patches of extra cell layers. (H) Hyperploid (Xcl1/xcl1/xcl1) leaf has a more severe extra cell layer phenotype than the diploid. (I) Homozygous diploid (Xcl1/Xcl1) leaf has the most severe extra cell phenotype. Scale bars A,B, 2 mm; C,I, 100 µm.

 


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  		Fig. 8. Model for the lineage-dependent differentiation of the extra cell layers produced by aberrant periclinal divisions. In wild-type leaf primordia, an acropetal gradient of cell division does not overlap with the basipetal cell differentiation gradient, allowing cells to perceive positional information for proper differentiation. In the Xcl1 mutant, the gradient of cell division competence is shifted up (possibly through the overproduction of Xcl1 gene product), allowing cell divisions to occur after differentiation signals have been perceived.

 

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© The Company of Biologists Ltd 2002