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 Byrne, M. E. Articles by Martienssen, R. A. Search for Related Content PubMed PubMed Citation Articles by Byrne, M. E. Articles by Martienssen, R. A.

ASYMMETRIC LEAVES1 reveals knox gene redundancy in Arabidopsis

Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA

View larger version (111K): [in a new window]   Fig. 1. Expression of LATERAL ORGAN BOUNDARIES (LOB) in as1 and as2. (A-C) Vegetative shoot of wild-type (A), as1 (B) and as2 (C). Compared with wild-type rosette leaves, which are elongate and spatulate in shape, as1 and as2 rosette leaves are round, lobed and with margins rolled under. (D-F) Side view and (G-I) top view of LOB GUS enhancer trap expression in the shoot apex of 8-day old seedlings. In wild-type (D,G) expression is restricted to a band of cells at the boundary between developing organ primordia and the SAM (arrow). In as1 seedlings (E,H) and as2 seedlings (F,I) little or no LOB expression is detected in the SAM. c, cotyledon; l, young leaf.

View larger version (62K): [in a new window]   Fig. 2. as1 and as2 suppress the stm mutant phenotype. Double mutants as1 stm-1 (A) and as2 stm-1 (B) have vegetative shoots and leaves similar to the single as1 and as2 mutants, respectively, but additional lateral shoots are formed in the place of flowers. Double mutants between the weak stm-2 allele with as1 (C) and as2 (D) produce more flowers. Scanning electron micrographs of flowers from as1 stm-2 (E) and as2 stm-2 (F) reveal that terminal flowers are frequently fused along the pedicel. Floral organs, particularly reproductive organs, are reduced in number or absent. Scale bar, 2 mm.

View larger version (80K): [in a new window]   Fig. 3. Class I knox genes in Arabidopsis. Dark shading indicates identical amino acids, light shading indicates conserved amino acids. The consensus sequence is shown below the alignments. The homeodomain is underlined. Amino acid changes in new bp alleles are marked above the sequence. Diamonds indicate single base changes resulting in an amino acid change to a stop codon in bp-6 and bp-7. In bp-8, D and * indicate single base changes leading to an amino acid substitution and creation of a stop codon, respectively. Two triplet nucleotide duplications result in amino acid insertions (N). An arrow marks the region where a Ds transposon disrupts KNAT2.

View larger version (71K): [in a new window]   Fig. 4. KNAT1 functions in SAM maintenance. (A-C) 8-day old whole seedlings of (A) wild type, with early vegetative leaves emerging, (B) the single stm-1 mutant and (C) the triple as1 stm-1 bp mutant. Both mutants have two cotyledons fused at the base and lack a vegetative shoot. (D- F) Longitudinal sections. (D) Wild type, showing dense staining cells of the SAM and young leaf primordia at the base of the cotyledons. At the base of the fused cotyledons in stm-1 (E) and as1 stm-1 bp (F) these cells are not found.

View larger version (72K): [in a new window]   Fig. 5. bp enhances the weak allele stm-2. The weak stm-2 mutant (A) produces a vegetative shoot with very few flowers. This phenotype is enhanced in the bp stm-2 double mutant (B) where a much reduced vegetative shoot or only a few, abnormal, leaves are formed.

View larger version (112K): [in a new window]   Fig. 6. as1 bp and as2 bp phenotypes are additive. (A-F) Whole plant phenotypes. Compared with wild-type (A), the single mutants bp (B), as1 (C) and as2 (E) are smaller in size. Double mutants as1 bp (D) and as2 bp (F) are smaller than any of the single mutants. Scale bar A-F, 4 cm. (G-R) Inflorescence and flower phenotypes. The short pedicels in bp (H,N) result in down-pointing flowers compared with wild type (G,M). In as1 (I,O) reduced sepals and petals expose the inner reproductive organs in young flowers. as1 bp flowers (J,P) have both short pedicels and reduced sepals and petals. as2 mutants have narrower sepals resulting in exposed inner floral organs in young flowers (K,Q). In the as2 bp double mutant (L,R) pedicels are short and sepals are reduced in size. Scale bar in M-R, 2 mm.

View larger version (60K): [in a new window]   Fig. 7. KNAT2 GUS reporter gene expression from the gene trap insertion GT7953. GUS reporter gene expression is observed in the embryonic (A) and seedling (B) SAM. In the inflorescence, GUS reporter gene expression is detected in the apex and young flowers but not in more mature flowers (C). Viewed under DIC microscopy (D), GUS activity (pink) is found in the inflorescence and floral meristems and in all organs of young flowers but in more mature flowers is confined to the carpels (inset). In as1 (E) and as2 (F), GUS reporter gene expression expands from the SAM into the base of the leaves. RT-PCR amplification using gene-specific primers and hybridization of products with gene-specific probes (G) show that KNAT2 transcripts are detected in wild type but not in plants homozygous for the gene trap insertion (top panel). RBC transcripts were ampilfied as a control (bottom panel).

View larger version (10K): [in a new window]   Fig. 8. A model of genetic interactions between stem cells and incipient leaf primordia in the SAM. STM represses AS1 and AS2 in stem cells and their immediate derivatives in the SAM. AS1 and AS2 together repress expression of KNAT1 and KNAT2 in organ primordia and may interact with each other. Expression of KNAT1 and KNAT2 is restricted to peripheral domains in the SAM. LOB is expressed in a region between the SAM and organ primordia and is activated by AS1-AS2 and KNAT1.