Abstract
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.
Highlights
In nature, plants unavoidably encounter environmental insults, including various abiotic and biotic stresses
A total of 1268 aldo-keto reductase (AKR) were identified in the 36 selected plant species after preliminary screening by the Hidden Markov Model (HMM) software package and verified by the Pfam, SMART, and NCBI databases (Supplementary Table S2)
galacturonic acid reductase (GalUR) homologs were revealed to be involved in the biosynthesis of ascorbic acid (AsA) from d-galacturonic acid in grapes and oranges [9,19]
Summary
Plants unavoidably encounter environmental insults, including various abiotic and biotic stresses. Under these situations, plants have developed a myriad of defense strategies. The aldo-keto reductases (AKR) gene was first identified to encode D-galacturonic acid reductase (GalUR) in a strawberry over 17 years ago and has been proved to play an important role in the AsA biosynthesis [5,6]. Transgenic tomato plants expressing strawberry GalUR had enhanced tolerance to abiotic stresses [8]. The GalUR homologs showed diverse expression patterns across different developmental stages in these two species, but only Citrus GalUR12 was significantly upregulated in fruit and could be confirmed as a contributor to AsA accumulation in orange fruit [9,11]
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