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First published online 1 November 2006
doi: 10.1242/dev.02652

Development 133, 4691-4698 (2006)
Published by The Company of Biologists 2006
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POL and PLL1 phosphatases are CLAVATA1 signaling intermediates required for Arabidopsis shoot and floral stem cells

Sang-Kee Song1,*, Myeong Min Lee2 and Steven E. Clark1,{dagger}

1 Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.
2 Department of Biology, Yonsei University, Sinchon 134, Seoul 120-749, Korea.


Figure 1
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  		Fig. 1. pol pll1 mutant tissue phenocopies wus mutants. (A,B) pol pll1 seedlings were not viable because of major defects in the basal embryo and vascular development compared with wild-type siblings (C,D). (B,D) Higher magnification of A and C, respectively. (E) pol pll1 apical tissue can be rescued by grafting to the hypocotyl and root of a wild-type seedling. (F-T) Grafted pol pll1 in the ER+ (F,K,P), er- (G,L,Q) and clv3-2 (H,M,R) backgrounds exhibited meristem termination similar to wus-1 mutants (I,N,S) during vegetative (F-J), inflorescence (K-O) and flower (P-T) development. (J,O,T) Wild-type Ler shown as a control. Similar meristem termination, albeit with reduced penetrance and expressivity, was observed in pol/pol pll1/+ plants (U,V), pol mutants expressing antisense PLL1 (W,X), and pol pll1 mutants incompletely rescued by PPLL1:PLL1 expression (Y). Arrows indicate junction of cotyledon vascular elements (B,D) or graft junction (E). Asterisks indicate flowers that developed with reduced or absent gynoecia. Insets in V and X show flowers with reduced or absent gynoecia, respectively, at higher magnifications.

 

Figure 2
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  		Fig. 2. pol pll1 mutations are epistatic to clv3. Mean number of organs from flowers of grafted pol pll1 in the er-, ER+ and clv3-2 backgrounds, wus-1 and clv3-2 mutants, and wild-type Ler plants. Error bars indicate standard error of the mean (s.e.m.). At least 50 flowers were counted for each mean.

 

Figure 3
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  		Fig. 3. pol pll1 tissue initiates, but does not maintain, WUS and CLV3 expression. (A-O) PWUS:GUS (A-F) and PCLV3:GUS (G-O) signal in pol pll1 seedlings germinated on MS media (G-I), inflorescence tissue from grafted pol pll1 plants (A-C,J-L), and phenotypically wild-type siblings (D-F,M-O). Each sample is shown at increasing magnifications to provide context for the location of the signal within the plant.

 

Figure 4
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  		Fig. 4. WUS expression rescues pol pll1 mutants. (A-D) Wild-type Ler (A), grafted pol pll1 (B,C) and wus-1 mutants (D) expressing PAP1:WUS (see text) all developed extensive meristem-like proliferations upon the transition to flowering (C and D shown at higher magnification). PCLV3:GUS activity in control (E) and PAP1:WUS (F) plants indicates a stem cell-like character for these proliferations, whereas PWUS:GUS activity is similar in control (G) and PAP1:WUS (H) plants. PER:WUS results in similar, but weaker, phenotypes in Ler (I) and pol pll1 grafted (J) plants.

 

Figure 5
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  		Fig. 5. PLL1 overexpression in clv mutants blocks differentiation. (A-P) clv2-1 (A,B,E,F,I,J) and clv3-2 (C,D,G,H,K-P) plants carrying P35S:PLL1 (A-D,N-P), PER:PLL1 (E-H) or no transgene (I-M) revealed massive accumulation of stem cells and a block of differentiation resulting from PLL1 overexpression. (A,C,E,G,I,K,M-O) At 10 days after germination; (B,D,F,H,J,L) 15 days after germination; (P) 6 days after germination. PCLV3:GUS (O) and PWUS:GUS (P) were expressed throughout the apices of clv3-2 P35S:PLL1 plants, indicating stem-cell character. Scale bars: 250 µm.

 

Figure 6
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  		Fig. 6. PLL1-overexpression effects are dependent on WUS. Mean number of organs from flowers of wus-1 and P35S:PLL1 wus-1 plants. Error bars indicate standard error of the mean (s.e.m.). In total, 93 wus-1 and 39 P35S:PLL1 wus-1 flowers were assayed. se, sepals; pe, petals; st; stamens; ca, carpels.

 




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