Análise evolucionária dos genes da oxidase terminal de plastídeo (PTOX) na subfamília Panicoideae

Abstract

Plastid terminal oxidases (PTOX) are key proteins in the chloroplast electron transport chain, acting in photoprotection and redox homeostasis in plants. While PTOX1 is associated with maintaining oxidative balance under mild to moderate stresses, PTOX2 predominates under extreme conditions (e.g., drought, salinity), promoting senescence via controlled production of reactive oxygen species (ROS). This functional dichotomy reflects critical adaptations for species predominant in high-temperature environments and adverse climatic conditions. This study investigates the evolutionary diversification of genes within the Panicoideae subfamily, selected due to its ecological and agricultural dominance, represented by strategic crops such as maize (Zea mays), sorghum (Sorghum bicolor), and sugarcane (Saccharum spp.), and its unique adaptations to water stress and photo-oxidative environments, such as C4 metabolism. To this end, we conducted in silico phylogenetic and structural analyses of the PTOX of 35 representative species from this subfamily, distributed across the Andropogoneae, Paniceae, and Paspaleae tribes, using genomic data available in the site NCBI repository. Protein-coding cDNA sequences for PTOX were obtained, and the protein sequence’s reading phase was verified using the Expasy Translate tool. Subsequently, a comparative analysis of exon/intron structure was performed using the Gene Structure Display Server (GSDS). Phylogenetic analysis was then conducted using Bayesian Inference to reconstruct the evolutionary relationships of PTOX’s genes within the Panicoideae subfamily. The results revealed remarkable structural conservation among PTOX’s genes, with a highly preserved gene organization (nine exons and eight introns), compatible with strong functional selective pressure. Phylogenetic analyses indicated the occurrence of a gene duplication event restricted to the Andropogoneae tribe, with subsequent retention of both copies in most species of the group. The two genes were identified on the same chromosome and separated by short genomic distances, pointing to a probable tandem duplication. Conversely, the Chrysopogoninae subtribe exhibited only one functional gene, suggesting secondary loss of PTOX2 after the ancestral duplication.