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First published online 13 August 2008
doi: 10.1242/dev.024273

Development 135, 3013-3019 (2008)
Published by The Company of Biologists 2008
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Floral meristem initiation and meristem cell fate are regulated by the maize AP2 genes ids1 and sid1

George Chuck1,*, Robert Meeley2 and Sarah Hake1

1 Plant Gene Expression Center, United States Department of Agriculture - Agriculture Research Service and the University of California, Albany, CA 94710, USA.
2 Pioneer - A DuPont Company, Johnston, IA 50131, USA.


Figure 1
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  		Fig. 1. Molecular analysis of maize sid1. (A) Amino acid alignment of maize SID1 (top) and IDS1 (bottom). Black line marks the AP2 domain. (B) Bayesian phylogram of DNA sequences of the AP2 domains of all MIR172-targeted genes from maize and rice. The Arabidopsis AP2 gene was used as the outgroup. (C) Genomic structure of the maize sid1 gene. Boxes represent exons, dark boxes represent the AP2 domain, and triangles represent Mutator transposon insertions. (D) RT-PCR of sid1 (top) and actin (bottom) from different tissues and tassels of ts4 mutant alleles. (E) Location of cleavage sites within sid1 from B73 ears (top) and ts4-TP ears (bottom). The number of clones cleaved at each different position within the microRNA binding site over the total number of clones analyzed is indicated; those in parentheses to the right indicate the number of clones cleaved 3' of the microRNA binding site. (F)3 RNA gel blot using 1 µg of poly(A)+ RNA from 0.5 cm tassels. Arrowheads mark positions of the 28S and 18S ribosomal RNAs. (G) RNA gel blot using 1 µg of poly(A)+ RNA from 0.5 cm ears. The 3' ends of ids1 and sid1 outside of the coding region for the AP2 domain were used as probes.

 

Figure 2
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  		Fig. 2. sid1/ids1 mutant phenotypes. (A) Tassels of maize ids1-Burr (left), sid1-mum3;ids1-Burr (middle) and ids1-mum1;sid1-mum1;ts4-A triple (right) mutants. (B) Mature ear of sid1-mum3;ids1-Burr. Bare rachis is present in place of missing rows. (C) Fertilized ears of sid1-mum3;ids1-Burr (left) compared with ids1-Burr (right). (D) Hand section of wild-type (WT) ear spikelet. (E) Hand section of ids1-mum1 ear spikelet. Extra florets are arranged laterally in the axils of bracts. (F) Hand section of sid1-mum3;ids1-Burr ear spikelet. Floret-like structure is terminal. (G) Isolated bract surrounding ovule of sid1-mum3;ids1-Burr ear spikelet showing silk transformation at tip. (H) Wild-type tassel spikelet showing two florets (arrowheads). (I) ids1-mum1 tassel spikelet with three florets (arrowheads). (J) sid1-mum3;ids1-Burr tassel spikelet showing absence of florets. (K) ts4-A;ids1-Burr double mutant tassel (left) and ear (right). The tip of the ear is highly branched. (L) Tassel of ts4-A;sid1-mum1 double mutant. (M) Tassel of plant that is homozygous for ts4-A and sid1-mum1 but heterozygous for ids1-mum1. (N) Ear of ts4-A;sid1-mum1 double mutant (left) and of ts4-A;sid1-mum1 double mutant heterozygous for ids1-mum1 (right). Plants are siblings.

 

Figure 3
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  		Fig. 3. Scanning electron microscopy of wild type, ids1-mum1 and ids1-mum1;sid1-mum3. (A) Wild-type maize tassel, side view. (B) Wild-type tassel, top view, showing seven rows of SPM (arrowheads). (C) Wild-type ear floret with initiating floral organs. Carpels are growing over the ovule primordium. (D) Older ear floret showing growing silk composed of fused carpels. (E) Top view of ids1-Burr ear showing six SPM rows (arrowheads). (F) ids1-Burr spikelets with florets in the axils of extra lemma bracts. (G) Older ids1-Burr spikelet with initiating floral organs. Floral organs initiate in a pattern similar to wild type. (H-M) ids1-Burr;sid1-mum4 double mutant. (H) Tassel primordium with a single BM (arrowhead). (I) Top view of tassel showing four rows of SPM (arrowheads). (J) Indeterminate male spikelets with multiple bracts and no florets. (K) Young ear primordium with four rows of SPM (arrowheads). (L) Female spikelet terminating in an ovule primordium. (M) Older female spikelet with bract-to-silk transformations. SPM, spikelet pair meristem; SM, spikelet meristem; BM, branch meristem; S, stamen; OP, ovule primordium; Le, lemma bract; LF, lower floret; Si, silk; F, floret; C, carpel. Scale bars: 100 µm.

 

Figure 4
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  		Fig. 4. In situ hybridization analysis of wild type, ts4 and ids1;sid1 mutants. Probes are listed at lower left of each panel, genotypes at lower right. (A-E) sid1 in situs. (A) Wild-type maize tassel primordium. (B) sid1-mum2 tassel primordium. (C) Wild-type ear florets with initiating floral organs. (D) ids-mum1 ear florets. (E) ts4-A ear inflorescence. (F-H) kn1 in situs. (F) Cross-section of ear of ids1-Burr. Arrowheads indicate rows. (G) Cross-section of ear of ids1-Burr;sid1-mum3. (H) Close-up of spikelet of double mutant showing prolonged kn1 expression. (I,J) bd1 in situs. Expression marked with arrowheads. (I) Longitudinal section of ids1-Burr;sid1-mum3 ear showing normal expression. (J) Older spikelets of double mutant showing prolonged expression. (K,L) zmm2 in situs. (K) Wild-type ear florets with initiating floral organs. (L) ids1-Burr;sid1-mum3 ear spikelets with ectopic expression in bracts and meristem. (M,N) zag1 in situs. (M) Wild-type ear florets with initiating floral organs. (N) ids1-Burr;sid1-mum3 ear spikelets with ectopic expression in bracts and meristem. Inset shows a younger stage. (O,P) silky1 in situs. (O) Wild-type ear florets with initiating floral organs. (P) ids1-Burr;sid1-mum3 ear spikelets showing no expression. Lo, lodicules.

 

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