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, 118 (2), 365-72

Eucalypt MADS-box Genes Expressed in Developing Flowers

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Eucalypt MADS-box Genes Expressed in Developing Flowers

S G Southerton et al. Plant Physiol.

Abstract

Three MADS-box genes were identified from a cDNA library derived from young flowers of Eucalyptus grandis W. Hill ex Maiden. The three egm genes are single-copy genes and are expressed almost exclusively in flowers. The egm1 and egm3 genes shared strongest homology with other plant MADS-box genes, which mediate between the floral meristem and the organ-identity genes. The egm3 gene was also expressed strongly in the receptacle or floral tube, which surrounds the carpels in the eucalypt flower and bears the sepals, petals, and numerous stamens. There appeared to be a group of genes in eucalypts with strong homology with the 3' region of the egm1 gene. The egm2 gene was expressed in eucalypt petals and stamens and was most homologous to MADS-box genes, which belong to the globosa group of genes, which regulate organogenesis of the second and third floral whorls. The possible role of these three genes in eucalypt floral development is discussed.

Figures

Figure 1
Figure 1
Diagrammatic median vertical section through a typical eucalypt flower before anthesis. c, Carpel; p, petal; pd, peduncle; r, receptacle; s, style; se, sepal; st, stamen. The fused sepals and fused petals, separately or fused together, form the operculum.
Figure 2
Figure 2
A comparison of the deduced aa sequences of the cDNAs egm1 (a), egm2 (b), and egm3 (c), with similar sequences from other plant species. The MADS-box is underlined and the K-box is in italics. Dots indicate aa identical to the particular egm reference sequence, and dashes indicate gaps in the sequence alignment. Numbers indicate aa position in the egm sequences.
Figure 3
Figure 3
A comparison of the deduced aa sequence of the MADS-box domain of the egm genes with the MADS-box domain of other plant genes. Dots indicate aa identical to the consensus sequence.
Figure 4
Figure 4
DNA gel-blot analysis of the egm genes. DNA isolated from E. grandis was digested with EcoRI, HindIII, or Xbal and hybridized with the egm gene minus the MADS-box under high stringency. Each lane contains 5 μg of digested genomic DNA.
Figure 5
Figure 5
Phylogenetic tree of several dicot MADS-box genes and the three eucalypt egm genes based on genetic distance analysis of the MIK region. The lengths of the horizontal branches are proportional to the number of base substitutions. Numbers next to the nodes indicate bootstrap values from 100 replicates. Nodes with <50% bootstrap support are collapsed.
Figure 6
Figure 6
Analysis of the expression of the egm genes in different eucalypt tissues. a, RNA gel-blot analysis of egm1, egm 2, and egm3 expression in roots, seedlings, stems, shoots, leaves, and flowers. b, RNA gel-blot analysis of egm2 and egm3 expression in floral receptacles, petals, stamens, carpels, and styles. The blots contained 10 μg of total RNA and were hybridized with 3′ regions of egm1, egm2, and egm3 genes. The lengths of each of the three egm messages are estimated at 1.1 kb.
Figure 7
Figure 7
RNA in situ-hybridization analysis of egm2 and egm3 expression in eucalypt flowers. B, Bract; C, carpel; F, floral meristem; P, petal; SE, sepal; S, stamen. Bar = 100 μm. A, Dark-field view of a longitudinal section through two E. grandis flowers, with developing petal, stamen, and carpel primordia hybridized to the egm1 gene probe. B, Dark-field view of a longitudinal section through an E. grandis flower initiating stamen primordia, hybridized to the egm2 gene probe. C, Dark-field view of a longitudinal section through two E. grandis flowers initiating petal primordia, hybridized to the egm2 gene probe. D, Bright-field view of a longitudinal section through two young E. grandis flowers with developing sepal primordia. E, Dark-field view of the section in D hybridized to the egm3 gene probe.

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