Despite the importance of secondary growth in plants, relatively few genes regulating this process have been identified to date. By using data from detailed transcript profiling of the poplar wood-forming tissues, 150 genes that are differentially expressed within the zone of secondary growth were identified. In order to determine the possible function of these poplar genes, potential Arabidopsis thaliana orthologs were identified and gene knockout lines analysed. Three selection filters were used to identify the most likely orthologous genes using poplar and Arabidopsis sequence comparisons, expression profiling in secondary thickened Arabidopsis hypocotyls and global expression analysis of Arabidopsis tissues. Three genes encoding AtCSLA2 (At5g22740), the AtGUT1 GT47 glycosyltransferase (At1g27440) and a protein with no proposed function AtUNKA (At4g27435) were selected for further detailed analysis of their role in secondary growth in Arabidopsis. The presented genome-based approach using both poplar and Arabidopsis systems provides powerful means towards assigning biological functions to enzymes with poorly understood biochemical activity, such as AtCSLA2 and AtGUT1, as well as for proteins with no known function.