Genome-wide identification, classification, and expression profiling of the aldehyde dehydrogenase gene family in pepper

Pepper (Capsicum annuum L.) is one of the most significant vegetable crops worldwide which is known for its pungency and nutritional value. The aldehyde dehydrogenase (ALDH) superfamily encompasses enzymes critical for the detoxification of toxic aldehydes into non-toxic carboxylic acids. A comprehensive genome-wide approach in pepper identified a total of 27 putative ALDH genes grouped into ten families based on the criteria of the ALDH gene nomenclature committee. Both segmental and tandem duplication assisted in the enhancement of CaALDH gene family members. The identified CaALDH members were found to be more closely related to the dicot plants, however, the members were distributed across the phylogenetic tree suggesting the pre-eudicot-monocot separation of the ALDH superfamily members. The gene structure and protein domain were found to be mostly conserved in separate phylogenetic classes, indicating that each family played an important role in evolution. Expression analysis revealed that CaALDHs were expressed in various tissues, developmental stages, and in response to abiotic stresses, indicating that they can play roles in plant growth, development, and stress adaptation. Interestingly, the majority of the CaALDH genes were found to be highly responsive to salinity stress, and only the CaALDH11A1 transcript showed upregulation in cold stress conditions. The presence of cis-acting elements in the promoter region of these genes might have a significant role in abiotic stress tolerance. Overall, these findings add to the current understanding, evolutionary history, and contribution of CaALDHs in stress tolerance, and smooth the path of further functional validation of these genes.