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First published online April 24, 2009
doi: 10.1242/10.1242/dev.033647

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Dual roles of the bZIP transcription factor PERIANTHIA in the control of floral architecture and homeotic gene expression

Annette T. Maier^1,*, Sandra Stehling-Sun^1,*,, Heike Wollmann¹, Monika Demar¹, Ray L. Hong^2,, Silke Haubeiß^1,, Detlef Weigel^1,2 and Jan U. Lohmann^1,3,¶

¹ Max-Planck Institute for Developmental Biology, D-72076 Tübingen, Germany.
² Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
³ University of Heidelberg, D-69120 Heidelberg, Germany.

View larger version (61K): [in this window] [in a new window]   Fig. 1. Requirement of AAGAAT box for AG enhancer activity. (A) Second AG intron. Flanking exons are indicated in gray. Conserved DNA elements are annotated according to Hong et al. (Hong et al., 2003). The 5' enhancer (green) contains a potential LFY-binding site (A) and the 33 bp AAGAAT box (dark green). The 3' enhancer (orange) contains two CArG boxes (C and E), and two linked CCAAT boxes (D). In addition, the 3' enhancer harbors two pairs of LFY/WUS-binding sites (F). For the reporters, regulatory sequences were linked to a minimal CaMV 35S promoter (red) and the coding region for bacterial β-glucuronidase (GUS; blue). RH146 has a 33 bp deletion of the sequence shown in Fig. 2A. (B) GUS activity in a primary inflorescence of a KB14 plant. (C) GUS expression was lost in RH146. (D) The distribution of GUS-positive plants among primary transformants (KB14, n=59; RH146, n=66).

View larger version (36K): [in this window] [in a new window]   Fig. 2. Characterization of AAGAAT-interacting factors. (A) Sequence of wild-type (wt) and mutated AAGAAT boxes. bZIP and GARP consensus motifs are indicated in green and orange, respectively. Mutated bases are in bold. (B) Yeast one-hybrid assays. The empty pEXPAD-502 vector was used as control. (C) Global expression profiles of candidate genes for AAGAAT-interacting factors. Mean normalized expression data are from the AtGenExpress developmental series (Schmid et al., 2005). Red, PAN; purple, bZIP21; light green, TGA5; yellow, TGA6; light blue, APL; light brown, UNE16; orange, At3g24120; dark blue, At4g37180; olive, ARR2.

View larger version (129K): [in this window] [in a new window]   Fig. 3. Expression, activity and phenotypes of PAN and AG. AG (A) and PAN (B) RNA expression in wild-type flowers. (C) PAN RNA was not detected in the pan mutant (Salk_057190 T-DNA insertion line). KB14 GUS expression in primary inflorescences of wild-type (D) and pan mutant (E) apices. White arrowheads point to flowers with AG::GUS activity; the black arrowhead indicates lack of staining in early pan flowers. (F) Point mutations in the bZIP-binding site abolished 5'AG enhancer activity. Floral morphologies of wild-type (G), pan mutant (H) and ag mutant (I) flowers grown in long-day conditions.

View larger version (40K): [in this window] [in a new window]   Fig. 4. Defects in pan mutant flowers from plants grown in short-day conditions. (A-F) Phenotypes of wild-type (A,C) and pan (B,D-F) flowers. Note determinacy defects in pan mutant (D and arrowheads in B). Scanning electron micrographs of weak (E) and intermediate (F) floral phenotypes of pan mutants. (G) Quantification of silique phenotypes (weak phenotype as in Fig. 4E and Fig. S5A in the supplementary material, intermediate as in Fig. 4F; see Figs S5B and S8 in the supplementary material). Fruits of the `undeveloped' category were patterned normally, but did not set seeds.

View larger version (111K): [in this window] [in a new window]   Fig. 5. Expression of AG and WUS in pan mutant flowers grown in short-day conditions. (A,B) AG RNA in early-stage (stage 5) wild-type (A) and pan (B) flowers. (C,D) AG RNA in wild-type (C) and pan (D) flowers in intermediate stages (stage 11-12) of development. AG RNA accumulated ectopically in flowers of pan mutants (white arrowheads in D). The black arrowhead in D highlights the meristem-like structure. (E,F) Expression of WUS RNA in wild-type (E) and pan (F) flowers in intermediate stages of development. The arrowhead in F highlights the meristem-like structure with WUS expression.

View larger version (149K): [in this window] [in a new window]   Fig. 6. Negative feedback between PAN, AG and WUS. (A,B) Expression of PAN RNA in wild-type (A) and ag mutant (B) flowers. The black arrowhead indicates declining PAN RNA levels in intermediate floral stages of wild type. The white arrowhead in B points to strong, persisting PAN expression in an ag mutant flower. (C) PAN RNA CLV3::WUS plants (SH57). (D) Distribution of AG RNA in the same CLV3::WUS flower as shown in C.

View larger version (19K): [in this window] [in a new window]   Fig. 7. Regulatory interactions between WUS, PAN and AG. WUS activates PAN and AG expression in a feed-forward loop. Once AG protein has accumulated it suppresses WUS transcription, which in turn leads to decreased PAN activation. In addition, AG might act on PAN regulation in a WUS-independent manner. Solid lines indicate known direct interactions, and dashed lines denote hypothetical regulatory mechanisms.

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