MdSCL8 as a Negative Regulator Participates in ALA-Induced FLS1 to Promote Flavonol Accumulation in Apples.

Haiwen Zhang,Liangju Wang,Yuyan An,Hao Yang,Guizhi Feng,Huihui Tao,Liuzi Zhang

doi:10.3390/ijms23042033

Haiwen Zhang, Liangju Wang + Show 5 more

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https://doi.org/10.3390/ijms23042033

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Abstract

Apples (Malus domestica) are rich in flavonols, and 5-aminolevulinic acid (ALA) plays an important role in the regulation of plant flavonoid metabolism. To date, the underlying mechanism of ALA promoting flavonol accumulation is unclear. Flavonol synthase (FLS) is a key enzyme in flavonol biosynthesis. In this study, we found that ALA could enhance the promoter activity of MdFLS1 in the ‘Fuji’ apple and improve its expression. With MdFLS1 as bait, we screened a novel transcription factor MdSCL8 by the Yeast One-Hybrid (Y1H) system from the apple cDNA library which we previously constructed. Using luciferase reporter assay and transient GUS activity assay, we verified that MdSCL8 inhibits the activity of MdFLS1 promoter and hinders MdFLS1 expression, thus reducing flavonol accumulation in apple. ALA significantly inhibited MdSCL8 expression. Therefore, ALA promoted the expression of MdFLS1 and the consequent flavonol accumulation probably by down-regulating MdSCL8. We also found that ALA significantly enhanced the gene expression of MdMYB22 and MdHY5, two positive regulators of MdFLS. We further demonstrated that MdMYB22 interacts with MdHY5, but neither of them interacts with MdSCL8. Taken together, our data suggest MdSCL8 as a novel regulator of MdFLS1 and provide important insights into mechanisms of ALA-induced flavonol accumulation in apples.

Highlights

Flavonol, a key class of secondary metabolites, plays important roles in preventing and treating human tumors, preventing cardiovascular diseases, lowering blood sugar and blood lipid, and resisting oxidation, viruses and allergies [1]
Since MdFLS1 is the key biosynthetic enzyme in apple flavonol biosynthesis, we investigated the effect of aminolevulinic acid (ALA) on MdFLS1 expression to explore how ALA regulates flavonol accumulation
We found that ALA significantly up-regulated MdFLS1 expression

Summary

Introduction

A key class of secondary metabolites, plays important roles in preventing and treating human tumors, preventing cardiovascular diseases, lowering blood sugar and blood lipid, and resisting oxidation, viruses and allergies [1]. Apples are rich in flavonol, the content of which accounts for 9.3% to 70.6% of total polyphenols [5]. Understanding flavonol biosynthesis regulation is crucial to improv fruit quality, increase nutritional value, and enhance environmental adaptability of apples. The biosynthesis of plant flavonoids begins with phenylalanine. It is catalyzed by enzymes such as Phenylalanine ammonia-lyase (PAL), Chalcone synthase (CHS), Chalcone isomerase (CHI), etc. FLS plays a key role in the biosynthesis of flavonol [6]. The expression level of FLS was proved to directly affect the content of flavonols in plants, such as petunia [7], citrus [8], grape [9], peach [10], blueberry [11], and apple [12]. The expression level of FLS is positively correlated with flavonol content

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