A Sequence Variation in GmBADH2 Enhances Soybean Aroma and Is a Functional Marker for Improving Soybean Flavor

Abstract

The vegetable soybean (<i>Glycine max</i> L. Merr.) plant is commonly consumed in Southeast Asian countries because of its nutritional value and desirable taste. A "pandan-like" aroma is an important value-added quality trait that is rarely found in commercial vegetable soybean varieties. In this study, three novel aromatic soybean cultivars with a fragrant volatile compound were isolated. We confirmed that the aroma of these cultivars is due to the potent volatile compound 2-acetyl-1-pyrroline (2AP) that was previously identified in soybean. A sequence comparison of <i>GmBADH1/2</i> (encoding an aminoaldehyde dehydrogenase) between aromatic and non-aromatic soybean varieties revealed a mutation with 10 SNPs and an 11-nucleotide deletion in exon 1 of <i>GmBADH2</i> in Quxian No. 1 and Xiangdou. Additionally, a 2-bp deletion was detected in exon 10 of <i>GmBADH2</i> in ZK1754. The mutations resulted in a frame shift and the introduction of premature stop codons. Moreover, genetic analyses indicated that the aromatic trait in these three varieties was inherited according to a single recessive gene model. These results suggested that a mutated <i>GmBADH2</i> may be responsible for the aroma of these three aromatic soybean cultivars. The expression and function of <i>GmBADH2</i> in aromatic soybean seeds were confirmed by qRT-PCR and CRISPR/Cas9. A functional marker developed on the basis of the mutated <i>GmBADH2</i> sequence in Quxian No. 1 and Xiangdou was validated in an F₂ population. A perfect association between the marker genotypes and aroma phenotypes implied that <i>GmBADH2</i> is a major aroma-conferring gene. The results of this study are potentially useful for an in-depth analysis of the molecular basis of 2-AP formation in soybean and the marker-assisted breeding of aromatic vegetable soybean cultivars.