MATE-Type Proteins Are Responsible for Isoflavone Transportation and Accumulation in Soybean Seeds.

Ming-Sin Ng,Liu Yang,Gyuhwa Chung,Yee-Shan Ku,Hon-Ming Lam,Wai-Shing Yung,Shikui Song,Chun-Kuen Man,Sau-Shan Cheng

doi:10.3390/ijms222112017

Abstract

Soybeans are nutritionally important as human food and animal feed. Apart from the macronutrients such as proteins and oils, soybeans are also high in health-beneficial secondary metabolites and are uniquely enriched in isoflavones among food crops. Isoflavone biosynthesis has been relatively well characterized, but the mechanism of their transportation in soybean cells is largely unknown. Using the yeast model, we showed that GmMATE1 and GmMATE2 promoted the accumulation of isoflavones, mainly in the aglycone forms. Using the tobacco BrightYellow-2 (BY-2) cell model, GmMATE1 and GmMATE2 were found to be localized in the vacuolar membrane. Such subcellular localization supports the notion that GmMATE1 and GmMATE2 function by compartmentalizing isoflavones in the vacuole. Expression analyses showed that GmMATE1 was mainly expressed in the developing soybean pod. Soybean mutants defective in GmMATE1 had significantly reduced total seed isoflavone contents, whereas the overexpression of GmMATE1 in transgenic soybean promoted the accumulation of seed isoflavones. Our results showed that GmMATE1, and possibly also GmMATE2, are bona fide isoflavone transporters that promote the accumulation of isoflavones in soybean seeds.

Highlights

While rich in proteins and oils, soybean seeds are uniquely rich in isoflavones, a group of naturally occurring phytoestrogens of high nutritional value
To test if GmMATE1 and GmMATE2 could transport isoflavones, a yeast uptake assay followed by quantification with ultra-performance liquid chromatography (UPLC) was performed
The coding sequences (CDSs) of GmMATE1 and GmMATE2 from the soybean accessions W05 and C08 were expressed in yeast, driven by the ADH1 promoter [31]

Summary

Introduction

While rich in proteins and oils, soybean seeds are uniquely rich in isoflavones, a group of naturally occurring phytoestrogens of high nutritional value. Isoflavones act as chemoattractants to Rhizobia for the induction of symbiosis [6] and work as phytoalexins against pests and pathogens [7]. Daidzein, and glycitein are the unmodified isoflavone aglycones. Aglycones are usually converted to the more stable glycosides (genistin, daidzin, and glycitin) and malonylglycosides (malonylgenistin, malonyldaidzin, and malonylglycitin) for storage (reviewed in [8]); these isoflavones are the most commonly found in soybean seeds [9]. IFS catalyses the oxidation of 40 ,7-dihydroxyflavanone (liquiritigenin) or 5,7,40 -trihydroxyflavanone (naringenin) to form intermediates which are converted to daidzein and genistein, respectively

Methods

Results

Conclusion