Phylogeny and expression profiling of CAD and CAD-like genes in hybrid Populus (P. deltoides x P. nigra): evidence from herbivore damage for subfunctionalization and functional divergence.
BACKGROUND
Cinnamyl Alcohol Dehydrogenase (CAD) proteins function in lignin biosynthesis and play a critical role in wood development and plant defense against stresses. Previous phylogenetic studies did not include genes from seedless plants and did not reflect the deep evolutionary history of this gene family. We reanalyzed the phylogeny of CAD and CAD-like genes using a representative dataset including lycophyte and bryophyte sequences. Many CAD/CAD-like genes do not seem to be associated with wood development under normal growth conditions. To gain insight into the functional evolution of CAD/CAD-like genes, we analyzed their expression in Populus plant tissues in response to feeding damage by gypsy moth larvae (Lymantria dispar L.). Expression of CAD/CAD-like genes in Populus tissues (xylem, leaves, and barks) was analyzed in herbivore-treated and non-treated plants by real time quantitative RT-PCR.


RESULTS
CAD family genes were distributed in three classes based on sequence conservation. All the three classes are represented by seedless as well as seed plants, including the class of bona fide lignin pathway genes. The expression of some CAD/CAD-like genes that are not associated with xylem development were induced following herbivore damage in leaves, while other genes were induced in only bark or xylem tissues. Five of the CAD/CAD-like genes, however, showed a shift in expression from one tissue to another between non-treated and herbivore-treated plants. Systemic expression of the CAD/CAD-like genes was generally suppressed.


CONCLUSIONS
Our results indicated a correlation between the evolution of the CAD gene family and lignin and that the three classes of genes may have evolved in the ancestor of land plants. Our results also suggest that the CAD/CAD-like genes have evolved a diversity of expression profiles and potentially different functions, but that they are nonetheless co-regulated under stress conditions.
Barakat
Abdelali
A
The School of Forest Resources, and The Huck Institutes of the Life Sciences, Pennsylvania State University, 324 Forest Resources Building, University Park, PA 16802, USA. aub14@psu.edu
Bagniewska-Zadworna
Agnieszka
A
Frost
Christopher J
CJ
Carlson
John E
JE
D000429:Alcohol Oxidoreductases / Q000235:genetics*; D000818:Animals; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D009036:Moths; D005810:Multigene Family; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics*; D032107:Populus / Q000201:enzymology / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013312:Stress, Physiological; D052584:Xylem / Q000378:metabolism
D018744:DNA, Plant; D010940:Plant Proteins; D000429:Alcohol Oxidoreductases; C018656:cinnamyl alcohol dehydrogenase