Molecular Evolutionary and Expression Pattern Analysis of AKR Genes Shed New Light on GalUR Functional Characteristics in Brassica rapa

The aldo-keto reductase (AKR) superfamily plays a major role in oxidation-reduction in plants. _D-galacturonic acid reductase (GalUR), an ascorbic acid (AsA) biosynthetic enzyme, belongs to this superfamily. However, the phylogenetic relationship and evolutionary history of the AKR gene family in plants has not yet been clarified. In this study, a total of 1268 AKR genes identified in 36 plant species were used to determine this phylogenetic relationship. The retention, structural characteristics, and expression patterns of AKR homologous genes in Brassica rapa and Arabidopsis thaliana were analyzed to further explore their evolutionary history. We found that the AKRs originated in algae and could be divided into A and B groups according to the bootstrap value; GalURs belonged to group A. Group A AKR genes expanded significantly before the origin of angiosperms. Two groups of AKR genes demonstrated functional divergence due to environmental adaptability, while group A genes were more conservative than those in group B. All 12 candidate GalUR genes were cloned, and their expression patterns under stress were analyzed, in Pak-choi. These genes showed an obvious expression divergence under multiple stresses, and BrcAKR22 exhibited a positive correlation between its expression trend and AsA content. Our findings provide new insights into the evolution of the AKR superfamily and help build a foundation for further investigations of GalUR's functional characteristics.

Keywords: AKR; Brassica rapa; GalUR; evolutionary history; expression pattern; selective pressure.