AgDHAR2, a chloroplast-located dehydroascorbate reductase, modulates the ascorbate accumulation and drought stress response in celery

Abstract

Celery is a vegetable crop with rich nutrition and economic value. It is easy to be affected by abiotic stress in its cultivation. Ascorbate (AsA) is considered as an important nutrient component in vegetable crops and an antioxidant for plants against abiotic stress. Dehydroascorbate reductase (DHAR) is a critical enzyme involved in AsA recycling. The study on the characteristics and functions of DHAR in celery were limited to date. Here, we identified a gene, AgDHAR2, encoding dehydroascorbate reductase from celery. AgDHAR2 was a chloroplast-localized protein and belonged to the member of glutathione S-transferases (GSTs) with conserved GST_N_3 and GST_C_2 domains. Transcript level of AgDHAR2 and the AsA accumulation in celery cvs. ‘Jinnan Shiqin’ and ‘Huangtaiji’ were induced under diverse stress conditions. Transgenic Arabidopsis thaliana and celery plants transformed with AgDHAR2 were generated to further investigate its role in AsA accumulation and drought stress response. Overexpression of AgDHAR2 in A. thaliana and celery led to elevated AsA contents and up-regulated AsA:DHA ratio. When subjected to drought stress, the progeny of transgenic A. thaliana plants hosting AgDHAR2 gene exhibited improved antioxidant-related genes expression, SOD and POD activities, proline accumulation and plant survival rates compared with wild-type plants, thereby showing higher drought tolerance. Taken together, the results of this study demonstrated that AgDHAR2 might contribute to enhanced drought tolerance through increasing AsA concentrations and maintaining redox state in celery.