Aldehyde Dehydrogenase Gene Superfamily in <i>Populus</i>: Organization and Expression Divergence between Paralogous Gene Pairs

Abstract

<div><p>Aldehyde dehydrogenases (ALDHs) constitute a superfamily of NAD(P)⁺-dependent enzymes that catalyze the irreversible oxidation of a wide range of reactive aldehydes to their corresponding nontoxic carboxylic acids. ALDHs have been studied in many organisms from bacteria to mammals; however, no systematic analyses incorporating genome organization, gene structure, expression profiles, and <i>cis</i>-acting elements have been conducted in the model tree species <i>Populus trichocarpa</i> thus far. In this study, a comprehensive analysis of the <i>Populus ALDH</i> gene superfamily was performed. A total of 26 <i>Populus ALDH</i> genes were found to be distributed across 12 chromosomes. Genomic organization analysis indicated that purifying selection may have played a pivotal role in the retention and maintenance of <i>PtALDH</i> gene families. The exon-intron organizations of <i>PtALDHs</i> were highly conserved within the same family, suggesting that the members of the same family also may have conserved functionalities. Microarray data and qRT-PCR analysis indicated that most <i>PtALDH</i>s had distinct tissue-specific expression patterns. The specificity of <i>cis</i>-acting elements in the promoter regions of the <i>PtALDHs</i> and the divergence of expression patterns between nine paralogous <i>PtALDH</i> gene pairs suggested that gene duplications may have freed the duplicate genes from the functional constraints. The expression levels of some <i>ALDHs</i> were up- or down-regulated by various abiotic stresses, implying that the products of these genes may be involved in the adaptation of <i>Populus</i> to abiotic stresses. Overall, the data obtained from our investigation contribute to a better understanding of the complexity of the <i>Populus ALDH</i> gene superfamily and provide insights into the function and evolution of <i>ALDH</i> gene families in vascular plants.</p></div