Genes duplicados da oxidase terminal do plastídio (PTOX) em soja [Glycine max L.) Merril]: caracterização, expressão e afinidade das isoformas proteicas pelo ligante

Abstract

Soybean [Glycine max (L.) Merril] occupies a prominent place in global economy, however, its productivity can be affected by environmental stresses and one way to solve the problem is developing molecular markers for use in breeding programs. Terminal oxidase of plastid (PTOX) is an enzyme found in chloroplasts of higher plants that catalyzes the oxidation of plastoquinol and the reduction of molecular oxygen to water. Several studies link PTOX to different types of stresses responses, therefore, to advance in understanding how protein expression regulation occurs in plant is necessary to the development of a potential molecular marker. Two genes encoding PTOX have been identified in soybean genome; however, their existence has not been proven experimentally, either there is not any data about the effects of these paralogs on the plant. The objective of the present study was to characterize and to analyze the expression profile of the two PTOX genes in G. max, and to investigate the affinity of the respective protein isoforms for the ligand. Initially, sequences encoding PTOX were identified and annotated in G. max and other legume species. Expression of PTOX genes was evaluated in several organs of G. max during development and under stress conditions by real-time PCR and by analyses of transcriptomic data available in GenBank. The modeling of the three-dimensional structures of the two protein isoforms was followed by molecular docking assay between the isoforms and their ligand. The results reveal that PTOX 1 and PTOX 2 genes are functional and expressed in practically all evaluated parts of the plant and have high similarity to each other. However, during the development of cotyledons, leaves and roots the expression profile of the genes is distinct. PTOX 1 prevails in younger organs whilst PTOX 2 increases expression as these organs age. Already under stressful conditions, PTOX 1 is generally positively regulated while PTOX 2 levels are down-regulated or remain stable. However, when a very severe stress is applied, the expression of PTOX 2 increases considerably. The affinity for the ligand also differed between the isoforms, being greater for PTOX 1. It is possible to conclude that PTOX genes duplication in soybean genome resulted in function gain to the plant. It is also suggested that PTOX 1 gene is associated with photosynthetic efficiency whereas PTOX 2 is related to leaf and cotyledon senescence.