Genome-wide characterization and expression analysis of the CINNAMYL ALCOHOL DEHYDROGENASE gene family in Triticum aestivum

Background CINNAMYL ALCOHOL DEHYDROGENASE (CAD) catalyzes the NADPH-dependent reduction of cinnamaldehydes into cinnamyl alcohols and is a key enzyme found at the final step of the phenylpropanoid pathway. Cinnamyl alcohols and their conjugates are subsequently polymerized in the secondary cell wall to form lignin. CAD genes are typically encoded by multi-gene families and thus traditionally organized into general classifications of functional relevance. Results In silico analysis of the hexaploid Triticum aestivum genome revealed 47 high confidence TaCAD copies, of which three were determined to be the most significant isoforms (class I) considered bone fide CADs . Class I CADs were expressed throughout development both in RNAseq data sets as well as via qRT-PCR analysis. In addition, Class I TaCADs were also upregulated after wounding and chitin elicitation in RNAseq data sets, but not in qRT-PCR experiments in roots or shoots. Of the 37 class II TaCADs identified, two groups were observed to be significantly co-expressed with class I TaCADs in developing tissue and under chitin elicitation in RNAseq data sets. These co-expressed class II TaCADs were also found to be phylogenetically unrelated to a separate clade of class II TaCADs previously reported to be an influential resistance factor to pathogenic fungal infection. Lastly, two groups were phylogenetically identified as class III TaCADs , which possess distinct conserved gene structures. However, the lack of data supporting their catalytic activity for cinnamaldehydes and their bereft transcriptional presence in lignifying tissues challenges their designation and function as CADs. Conclusions Taken together, the TaCAD gene family contributes overlapping but nonredundant functions that likely contribute to T. aestivum growth across a wide variety of agroecosystems and tolerance to a large variety of stressors.