QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by McSteen, P. Articles by Hake, S. Search for Related Content PubMed PubMed Citation Articles by McSteen, P. Articles by Hake, S. Social Bookmarking                         What's this?

barren inflorescence2 regulates axillary meristem development in the maize inflorescence

Plant Gene Expression Center, Agricultural Research Service – USDA, 800 Buchanan St, Albany, CA 94710, USA and Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA

View larger version (28K): [in a new window]   Fig. 1. Diagram of a normal tassel and spikelet pair. (A) Diagram of a normal tassel (male inflorescence). The tassel consists of a central main spike with long lateral branches at the base. Short branches called spikelet pairs cover the main spike and the lateral branches. (B) Diagram of a spikelet pair from a normal tassel. The pedicellate spikelet is borne on a pedicel while the sessile spikelet is attached at the base. Each spikelet contains two florets, the upper floret (uf) and the lower floret (lf) enclosed by two glumes, the inner glume (ig) and the outer glume (og). Each floret consists of lemma (l), palea (p), two lodicules (not shown) and three stamens (st).

View larger version (23K): [in a new window]   Fig. 2. bif2 mutants make fewer branches and spikelets in a background-dependent manner. (A) Normal tassel after anthesis (B73 genetic background). The main spike and long lateral branches produce pairs of spikelets. (B) bif2 mutant tassel in the B73 genetic background. In severe cases, bif2 mutants produce no branches and almost no spikelets, resulting in a barren rachis (inflorescence stem). (C) bif2 mutant tassel in the A188 genetic background. The tassel has a sparse appearance with few branches and few spikelets on the branches and main spike. (D) bif2 mutant tassel in the A619 genetic background. Single spikelets form on the rachis. The tip of the rachis is split. (E) Normal ear (the female inflorescence). The outer protective husk leaves are removed to reveal rows of female florets with elongated silks covering the rachis. (F) bif2 mutant ear. Inside the husk leaves is a bare rachis with no spikelets or florets. The tip of the rachis is split. Scale bar, 2.7 cm.

View larger version (100K): [in a new window]   Fig. 3. bif2 is required for branch meristem formation: scanning electron micrographs (SEM) of normal and bif2 mutant inflorescences. (A) A normal male inflorescence at 5-weeks old. The inflorescence meristem (im) produces axillary meristems called branch meristems (bm) which then form two spikelet meristems (sm). (B) A bif2 male inflorescence at 5-weeks old. The inflorescence meristem fails to produce branch meristems. Ripples are visible on the surface of the rachis. (C) A normal female inflorescence at 8 weeks of age. The higher magnification shows that branch meristems (bm) form in the axils of bract primordia (br), which are suppressed. (D) A bif2 female inflorescence at 8 weeks. The ripples on the surface of the rachis resemble bract primordia. Bm, branch meristem; br, bract primordium; sm, spikelet meristem; im, inflorescence meristem. Scale bar, 200 µm.

View larger version (99K): [in a new window]   Fig. 4. bif2 is required for branch meristem formation: histological analysis of normal and bif2 mutant inflorescences. (A) Longitudinal section of a normal female inflorescence stained with TBO. The apex and the periphery of the inflorescence meristem (im) stain intensely. Branch meristems (bm) form densely staining bulges in the axils of less densely stained bract primordia (br). Scale bar, 80 µm. (B) Higher magnification of A. The branch meristem is visible as several densely staining cell layers. Scale bar, 250 µm. (C) Longitudinal section of a bif2 female inflorescence stained with TBO. Like normal inflorescences, the inflorescence apex and periphery are densely stained, but branch meristems do not bud from the axils of bract primordia as in wild type. Scale bar, 80 µm. (D) Higher magnification of bif2 bract primordia (from C) showing that several densely staining cells are visible on the adaxial side of the bract primordium (ad) though the staining does not extend through as many cell layers as normal. Note that bif2 bract primordia are larger than normal bract primordia. Scale bar, 250 µm. ad, adaxial side of bract primordium; bm, branch meristem; br, bract primordium; im, inflorescence meristem.

View larger version (108K): [in a new window]   Fig. 5. bif2 is required for branch meristem formation: expression analysis with kn1. (A) RNA in situ hybridization of kn1 in a normal male inflorescence. kn1 is strongly expressed in the inflorescence meristem (im) and is downregulated on the flanks of the inflorescence as bract primordia initiate (br). Branch meristem initials (bi) are visible as a small group of kn1-expressing cells separating successive bract primordia. kn1 is highly expressed in branch meristems (bm) as they grow out. (B) kn1 RNA in situ hybridization in a bif2 male inflorescence. In this example, the inflorescence apex is fasciated and has split into two growing points. As in normal inflorescences, kn1 is expressed in the inflorescence meristem and is downregulated as bract primordia (br) initiate. Unlike normal, kn1 is not expressed on the flanks of the inflorescence and there is no evidence of branch meristem formation or branch meristem initials. (C) Immunolocalization of KN1 protein in a bif2 male inflorescence. KN1 protein is found in the inflorescence meristem but not on the flanks of the meristem. Note that KN1 protein extends into the epidermal layer of the inflorescence meristem (Smith et al., 1992; Jackson et al., 1994). (D) kn1 RNA in situ hybridization in a normal female inflorescence. kn1 is expressed in the inflorescence (im), branch (bm) and spikelet meristems (sm) as well as in the stem and vasculature. (E) kn1 RNA in situ hybridization in a bif2 female inflorescence. kn1 RNA is not present on the flanks of the inflorescence owing to the absence of branch, spikelet and floral meristems. (F) kn1 RNA in situ hybridization in a fasciated bif2 female inflorescence. Down regulation of kn1 within the inflorescence meristem occurs when the inflorescence apex has split into separate growing points. Bi, branch meristem initials, bm, branch meristem; br, bract primordium; im, inflorescence meristem;,sm, spikelet meristem. Scale bars, (A-C) 100 µm; (D-F) 300 µm.

View larger version (30K): [in a new window]   Fig. 6. bif2 is required for branch meristem formation: double mutant analysis with tsh and ts4. (A) At the base of the tsh mutant tassel, large bracts (br) subtend the long branches (b). Scale bar, 3.33 cm. (B) At the base of the bif2;tsh double mutant tassel, large bracts (br) form but no branches are produced in the axils of the bracts. Scale bar, 3.33 cm. (C) On the main spike of the tsh mutant tassel, small bracts (br) subtend the spikelet pairs (sp). Scale bar, 0.7cm. (D) On the main spike of the bif2;tsh double mutant tassel, small bracts are produced as in tsh mutants, however, no spikelet pairs form in the axils of the bracts as in bif2 mutants. Scale bar, 0.6 cm. (E) ts4 mutant tassels are highly branched because of a delay in the transition from branch to spikelet meristem identity (Irish, 1997). Scale bar, 1.8cm. (F) The bif;ts4 double mutant tassel has the same phenotype as a bif2 mutant tassel. Note that in this case, the bif2 mutant phenotype is severe and the tip of the rachis is fasciated. Scale bar,1.8 cm. B, branch; br, derepressed bract leaf; sp, spikelet pair.

View larger version (29K): [in a new window]   Fig. 7. bif2 is required for branch meristem maintenance: double mutant analysis with ra1. (A) In ra1 mutant tassels, spikelet pairs are converted to branches resulting in a highly branched tassel (Gernart, 1912). Scale bar, 3.33 cm. (B) bif2;ra1 double mutant tassels have a similar phenotype to bif2 mutants, except that when branches form they have more spikelets than bif2 mutants. (C) bif2 mutant tassel. In this genetic background, the bif2 mutant phenotype is weak and single spikelets form on the main spike. D to G are branches dissected from midway along the main spike of a family segregating normal (D), bif2 (E), bif2;ra1 (F) and ra1 (G) mutant plants. Scale bar, 600 µm. (D) Normal spikelet pair with pedicellate and sessile spikelet. (E) bif2 mutant spikelet. Note that bif2 mutants produce spikelets singly instead of in pairs and that the pedicel is elongated. (F) bif2;ra1 double mutant branch with several spikelets. G) ra1 mutant branch with many spikelets.

View larger version (34K): [in a new window]   Fig. 8. bif2 is required for spikelet and floral meristem maintenance. (A) Normal spikelet dissected open to reveal the two florets. The lower floret (lf) is flanked by the outer glume (og) and the upper floret (uf) is flanked by the inner glume (ig). Each floret consists of a lemma (l; flanked by the glume), palea (p; separating the flowers), lodicules (not visible) and three stamens (st). Scale bar, 230 µm. (B) bif2 spikelet. The upper floret consists of lemma and palea only while the lower floret is normal. Scale bar, 230 µm. (C) bif2 spikelet. The upper floret is replaced by a filamentous structure (f) and the lower floret has two stamens instead of three. Note that the stamens are deformed. Scale bar, 210 µm. (D) bif2 spikelet consisting of only two glumes and two leaf-like structures that resemble the lemma or palea. Scale bar, 260 µm. (E) Floral organ numbers were counted from florets dissected from 103 spikelets of a bif2 mutant and from 100 spikelets of a normal sibling. Normal florets have a lemma, palea, two lodicules (not counted) and three stamens in both upper and lower florets. bif2 mutants produce fewer organs in both the upper and lower floret, though the upper floret is more severely affected than the lower floret. The percentages refer to the number of florets with the complement of organs shown in the diagram. Green bar, filamentous structure; star, other (florets with lemma and three stamens or palea and one stamen); dash, no floret.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter