Genome-Wide Identification of WUSCHEL-Related Homeobox (WOX) Gene Family in Hazelnut (Corylus avellana L.) and Their Expression Profiles During Adventitious Root Development

Abstract The propagation of high-yield and high-quality hazelnut varieties through vegetative methods, such as micropropagation, is crucial for large-scale production. However, low adventitious root (AR) formation and regeneration remain major limitations in hazelnut micropropagation. AR formation is regulated by various environmental and internal factors, with the WUSCHEL-related homeobox (WOX) gene family playing a central role in its molecular control. Although WOX transcription factors (TFs) are known regulators of AR development in several plant species, this gene family has not yet been characterized in hazelnut. In this study, a genome-wide analysis identified WOX gene family members in hazelnut and examined their roles in AR development. Ten CaWOX genes were unevenly distributed across six chromosomes. Phylogenetic analysis grouped these proteins into three clades (WUS, intermediate, and ancient), consistent with other plant species. Conserved motif analysis revealed structural similarity among CaWOX proteins. The proteins ranged from 167 to 351 amino acids with molecular weights of 19.10–40.20 kDa, and three had isoelectric points below 7. All CaWOX proteins were predicted to localize in the nucleus. Promoter analysis revealed cis-acting regulatory elements associated with hormone signaling, development, and stress responses, indicating complex transcriptional regulation. CaWOX4 transcripts showed a statistically significant 1.82-fold increase on day 7 compared to day 1, whereas CaWOX13 transcripts showed a 1.36-fold increase that was not statistically significant. Overall, these results suggest that CaWOX4 and CaWOX13 may be associated with AR formation in hazelnut and represent candidate genes for future functional studies aimed at improving rooting efficiency in woody plants with recalcitrant regeneration systems.