_Faakr23_ Modulates Ascorbic Acid and Anthocyanin Accumulation in Strawberry (_Fragaria \(\times\) ananassa_) Fruits  
[PERSON] Institute of Forestry and Pomology, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100093  
dehydrogenase (l-GalDH), and l-galactono-1,_A_-lactone dehydrogenase (l-GalLDH) [5]. In addition, the D-galacturonic acid (d-GalUA) pathway is another validated AsA biosynthetic pathway in plants; it was first identified in strawberry plants [5; 6]. In 2003, researchers isolated the gene encoding d-GalUA reductase (_FaGalUR_) that catalyzes a key step in the d-GalUA pathway [6]. Overexpression of _FaGalUR_ in _Arabidopsis_, potato, and tomato led to a 2-3-fold increase in AsA content in the transgenic plant leaves and fruits compared with control [6; 7; 8]. These results indicate that _FaGalUR_ plays a significant role in AsA biosynthesis and can be used as a target to improve AsA content in strawberry fruits by genome editing [9; 10]. Anthocyanin is the major pigment contributing to strawberry fruit coloring, which influences the commodity and nutritive value of strawberries. Moreover, anthocyanin is important antioxidant in plants, and it plays a key role in exogenous stress tolerance [11]. The biosynthesis of anthocyanin is carried out by a series of enzymes, including phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate coenzyme A ligase (4 CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavonoid 3-hydroxylase (F3H), dihydronlavond-4-Reductase (DFR), anthocyanin synthase (ANS), and UDP-glycoseflavonoid 3-O-glycostransferase (UFGT); they cooperatively synthesize anthocyanin [12]. To date, a number of transcription factors have been verified to participate in the accumulation of anthocyanin in strawberries, such as _FaMYB10_, _FaGAMYB_, _FaMYB9/11_, _FabHLH3_, _FaTTG1_, _FaRAVI_, _FaMADS1a_, _FaMADS9_, _FaRAP_, and _FaRIF_[13; 14; 15; 16; 17; 18; 19; 20; 21]. Besides these transcription factors, some important regulatory proteins regulate the level of anthocyanin, namely, protein phosphatase ABI1, protein kinase FaSnRK2.6, FaMRLK47, and FvMAPK3 [22; 23; 24; 25]. Aldo-keto reductases (AKRs) are a superfamily of NADH-dependent oxidoreductase-tases, including aldehyde reductase, aldose reductase and xylose reductase [26]. AKRs are found in animals, plants, and bacteria and regulate cell oxidation reduction (redox) under multiple stress conditions. In mice, _AKR1A_ performs the function of glucuronolactone reductase; knockout _AKR1A_ induces the lack of AsA in mice [27], which indicates that _AKR1A_ might participate in AsA biosynthesis in mice. In plants, AKRs plays an important role in the accumulation of antioxidants and stress tolerance [28; 29]; for instance, AKR family member _FaGalUR_ is an important enzyme in the d-GalUA pathway for AsA synthesis [6]. [PERSON] et al. cloned a NADPH-dependent AKR family gene, _MsALR_, in alfalfa; the heterologous expression of _MsALR_ in tobacco significantly improved its tolerance to herbicide and redox damage caused by heavy metals [29]. In rice and tobacco, the overexpression of _PsAKR_ or _OsAKR1_ prominently increased herbicide resistance [30], and the transgenic tobacco contained higher glutathione, reducing the H\({}_{2}\)O\({}_{2}\) level, elevating the chlorophyll content, and, finally, enhancing salt tolerance [31]. In peach (_Prunus persica_), expression of the aldo-keto reductase gene _PpAKR1_ was induced by ABA, oxidative stress, low temperature, and salt stress; furthermore, _PpAKR1_ enhanced salt resistance [32]. According to our previous work, _FaAKR23_ was identified as the most dramatically increased _FaAKR_ gene during fruit development and ripening in cultivated strawberries [33]. However, little is known about how it regulates fruit ripening and quality formation, especially antioxidant accumulation. In this study, we first clarify that _FaAKR23_ is a regulator of AsA and anthocyanin accumulation in strawberry fruits.