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The cinnamyl alcohol dehydrogenase gene family in Populus: phylogeny, organization, and expression.

Barakat A, Bagniewska-Zadworna A, Choi A, Plakkat U, DiLoreto DS, Yellanki P, Carlson JE - BMC Plant Biol. (2009)

Bottom Line: CAD genes associated with xylem development (PoptrCAD 4 and PoptrCAD 10) belong to Class I and Class II.The duplication of several CAD genes seems to be associated with a genome duplication event that happened in the ancestor of Salicaceae.Phylogenetic analyses associated with expression profiling and results from previous studies suggest that CAD genes involved in wood development belong to Class I and Class II.

View Article: PubMed Central - HTML - PubMed

Affiliation: The School of Forest Resources, The Huck Institutes of the Life Sciences, Pennsylvania State University, 324 Forest Resources Building, University Park, PA 16802, USA. aub14@psu.edu

ABSTRACT

Background: Lignin is a phenolic heteropolymer in secondary cell walls that plays a major role in the development of plants and their defense against pathogens. The biosynthesis of monolignols, which represent the main component of lignin involves many enzymes. The cinnamyl alcohol dehydrogenase (CAD) is a key enzyme in lignin biosynthesis as it catalyzes the final step in the synthesis of monolignols. The CAD gene family has been studied in Arabidopsis thaliana, Oryza sativa and partially in Populus. This is the first comprehensive study on the CAD gene family in woody plants including genome organization, gene structure, phylogeny across land plant lineages, and expression profiling in Populus.

Results: The phylogenetic analyses showed that CAD genes fall into three main classes (clades), one of which is represented by CAD sequences from gymnosperms and angiosperms. The other two clades are represented by sequences only from angiosperms. All Populus CAD genes, except PoptrCAD 4 are distributed in Class II and Class III. CAD genes associated with xylem development (PoptrCAD 4 and PoptrCAD 10) belong to Class I and Class II. Most of the CAD genes are physically distributed on duplicated blocks and are still in conserved locations on the homeologous duplicated blocks. Promoter analysis of CAD genes revealed several motifs involved in gene expression modulation under various biological and physiological processes. The CAD genes showed different expression patterns in poplar with only two genes preferentially expressed in xylem tissues during lignin biosynthesis.

Conclusion: The phylogeny of CAD genes suggests that the radiation of this gene family may have occurred in the early ancestry of angiosperms. Gene distribution on the chromosomes of Populus showed that both large scale and tandem duplications contributed significantly to the CAD gene family expansion. The duplication of several CAD genes seems to be associated with a genome duplication event that happened in the ancestor of Salicaceae. Phylogenetic analyses associated with expression profiling and results from previous studies suggest that CAD genes involved in wood development belong to Class I and Class II. The other CAD genes from Class II and Class III may function in plant tissues under biotic stresses. The conservation of most duplicated CAD genes, the differential distribution of motifs in their promoter regions, and the divergence of their expression profiles in various tissues of Populus plants indicate that genes in the CAD family have evolved tissue-specialized expression profiles and may have divergent functions.

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Lignification pattern in Populus tissues selected for qRT-PCR studies. Far left column displays organs and tissues used (Leaf blade, Petiole, bark, Xylem). Middle column shows lignin deposition, visualized under the light microscope after phloroglucine-HCl staining (red color). Right column shows lignin distribution by fluorescent microscopy (autofluorescence). a, b – cross section of leaf vascular bundle, c, d – petiole cross section, e, f – transverse section of stem segment, g, h – secondary xylem from stem. Abbreviations: x – xylem, ph – phloem, s – schlerenchyma. Bars = 100 μm.
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Figure 4: Lignification pattern in Populus tissues selected for qRT-PCR studies. Far left column displays organs and tissues used (Leaf blade, Petiole, bark, Xylem). Middle column shows lignin deposition, visualized under the light microscope after phloroglucine-HCl staining (red color). Right column shows lignin distribution by fluorescent microscopy (autofluorescence). a, b – cross section of leaf vascular bundle, c, d – petiole cross section, e, f – transverse section of stem segment, g, h – secondary xylem from stem. Abbreviations: x – xylem, ph – phloem, s – schlerenchyma. Bars = 100 μm.

Mentions: Before analyzing the expression of CAD genes using Real time RT-PCR, we analyzed lignin deposition patterns in the tissues of plants by staining with phloroglucinol and observation by light and fluorescent microscopy. The lignin distribution pattern under UV light was similar to that of staining with acidified phloroglucinol, indicating that the same tissues were lignified. In leaf tissues lignin was detected mainly in the xylem of vascular bundles and in schlerenchyma fibers surrounding vascular tissues (Fig. 4a, b). Petioles were lignified only in secondary cell walls of xylem and in the extensive hypodermal band of schlerenchyma (Fig. 4c, d). The most heavily lignified tissues were observed in stem segments. The bark of the stem, including phloem sieve tube cells, and parenchyma were not lignified (Fig. 4e). In the bark, lignin was detected only in schlerenchyma fibers at the outer part of phloem (Fig. 4e, f). Secondary xylem with thickened secondary cell walls showed the strongest reaction, demonstrating large amounts of lignin distributed in the tracheary vessels and fibers (Fig. 4g, h).


The cinnamyl alcohol dehydrogenase gene family in Populus: phylogeny, organization, and expression.

Barakat A, Bagniewska-Zadworna A, Choi A, Plakkat U, DiLoreto DS, Yellanki P, Carlson JE - BMC Plant Biol. (2009)

Lignification pattern in Populus tissues selected for qRT-PCR studies. Far left column displays organs and tissues used (Leaf blade, Petiole, bark, Xylem). Middle column shows lignin deposition, visualized under the light microscope after phloroglucine-HCl staining (red color). Right column shows lignin distribution by fluorescent microscopy (autofluorescence). a, b – cross section of leaf vascular bundle, c, d – petiole cross section, e, f – transverse section of stem segment, g, h – secondary xylem from stem. Abbreviations: x – xylem, ph – phloem, s – schlerenchyma. Bars = 100 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2662859&req=5

Figure 4: Lignification pattern in Populus tissues selected for qRT-PCR studies. Far left column displays organs and tissues used (Leaf blade, Petiole, bark, Xylem). Middle column shows lignin deposition, visualized under the light microscope after phloroglucine-HCl staining (red color). Right column shows lignin distribution by fluorescent microscopy (autofluorescence). a, b – cross section of leaf vascular bundle, c, d – petiole cross section, e, f – transverse section of stem segment, g, h – secondary xylem from stem. Abbreviations: x – xylem, ph – phloem, s – schlerenchyma. Bars = 100 μm.
Mentions: Before analyzing the expression of CAD genes using Real time RT-PCR, we analyzed lignin deposition patterns in the tissues of plants by staining with phloroglucinol and observation by light and fluorescent microscopy. The lignin distribution pattern under UV light was similar to that of staining with acidified phloroglucinol, indicating that the same tissues were lignified. In leaf tissues lignin was detected mainly in the xylem of vascular bundles and in schlerenchyma fibers surrounding vascular tissues (Fig. 4a, b). Petioles were lignified only in secondary cell walls of xylem and in the extensive hypodermal band of schlerenchyma (Fig. 4c, d). The most heavily lignified tissues were observed in stem segments. The bark of the stem, including phloem sieve tube cells, and parenchyma were not lignified (Fig. 4e). In the bark, lignin was detected only in schlerenchyma fibers at the outer part of phloem (Fig. 4e, f). Secondary xylem with thickened secondary cell walls showed the strongest reaction, demonstrating large amounts of lignin distributed in the tracheary vessels and fibers (Fig. 4g, h).

Bottom Line: CAD genes associated with xylem development (PoptrCAD 4 and PoptrCAD 10) belong to Class I and Class II.The duplication of several CAD genes seems to be associated with a genome duplication event that happened in the ancestor of Salicaceae.Phylogenetic analyses associated with expression profiling and results from previous studies suggest that CAD genes involved in wood development belong to Class I and Class II.

View Article: PubMed Central - HTML - PubMed

Affiliation: The School of Forest Resources, The Huck Institutes of the Life Sciences, Pennsylvania State University, 324 Forest Resources Building, University Park, PA 16802, USA. aub14@psu.edu

ABSTRACT

Background: Lignin is a phenolic heteropolymer in secondary cell walls that plays a major role in the development of plants and their defense against pathogens. The biosynthesis of monolignols, which represent the main component of lignin involves many enzymes. The cinnamyl alcohol dehydrogenase (CAD) is a key enzyme in lignin biosynthesis as it catalyzes the final step in the synthesis of monolignols. The CAD gene family has been studied in Arabidopsis thaliana, Oryza sativa and partially in Populus. This is the first comprehensive study on the CAD gene family in woody plants including genome organization, gene structure, phylogeny across land plant lineages, and expression profiling in Populus.

Results: The phylogenetic analyses showed that CAD genes fall into three main classes (clades), one of which is represented by CAD sequences from gymnosperms and angiosperms. The other two clades are represented by sequences only from angiosperms. All Populus CAD genes, except PoptrCAD 4 are distributed in Class II and Class III. CAD genes associated with xylem development (PoptrCAD 4 and PoptrCAD 10) belong to Class I and Class II. Most of the CAD genes are physically distributed on duplicated blocks and are still in conserved locations on the homeologous duplicated blocks. Promoter analysis of CAD genes revealed several motifs involved in gene expression modulation under various biological and physiological processes. The CAD genes showed different expression patterns in poplar with only two genes preferentially expressed in xylem tissues during lignin biosynthesis.

Conclusion: The phylogeny of CAD genes suggests that the radiation of this gene family may have occurred in the early ancestry of angiosperms. Gene distribution on the chromosomes of Populus showed that both large scale and tandem duplications contributed significantly to the CAD gene family expansion. The duplication of several CAD genes seems to be associated with a genome duplication event that happened in the ancestor of Salicaceae. Phylogenetic analyses associated with expression profiling and results from previous studies suggest that CAD genes involved in wood development belong to Class I and Class II. The other CAD genes from Class II and Class III may function in plant tissues under biotic stresses. The conservation of most duplicated CAD genes, the differential distribution of motifs in their promoter regions, and the divergence of their expression profiles in various tissues of Populus plants indicate that genes in the CAD family have evolved tissue-specialized expression profiles and may have divergent functions.

Show MeSH