Characteristic of the Ascorbate Oxidase Gene Family in and Analysis of the Role of AAO in Response to Salinity and Drought in Beet.

Ascorbate oxidase, which is known to play a key role in regulating the redox state in the apoplast, cell wall metabolism, cell expansion and abiotic stress response in plants, oxidizes apo-plastic ascorbic acid (AA) to dehydroascorbic acid (DHA). However, there is little information about the AAO genes and their functions in beets under abiotic stress. The term salt or drought stress refers to the treatment of plants with slow and gradual salinity/drought. Contrastingly, salt shock consists of exposing plants to high salt levels instantaneously and drought shock occurs under fast drought progression. In the present work, we have subjected plants to salinity or drought treatments to elicit either stress or shock and carried out a genome-wide analysis of ascorbate oxidase (AAO) genes in sugar beet cv. Huzar) and its halophytic ancestor . Here, conserved domain analyses showed the existence of twelve AAO gene family members in the genome of sugar beet. The AAO_1-12 genes are located on chromosomes 4, 5, 6, 8 and 9. The phylogenetic tree exhibited the close relationships between AAO_1-12 and AAO genes of and . In both beet genotypes, downregulation of AAO gene expression with the duration of salt stress or drought treatment was observed. This correlated with a decrease in AAO enzyme activity under defined experimental setup. Under salinity, the key downregulated gene was AAO_10 in and under drought the AAO_3 gene in both beets. This phenomenon may be involved in determining the high tolerance of beet to salinity and drought.