Improving the Aroma of Millets by Targeting the Betaine Aldehyde Dehydrogenase 2 Gene: A Promising Approach for Popularising Millet Foods Worldwide

Millets are highly nutritious and traditional staple foods consumed by millions worldwide. However, their low palatability and limited aroma have restricted their broader acceptance in human diets. Aroma is a key trait influencing consumer preference, and in many crops, 2-acetyl-1- pyrroline (2AP) contributes significantly to fragrance and palatability. The betaine aldehyde dehydrogenase 2 (BADH2) gene is a critical regulator of 2AP biosynthesis in crops. Targeted manipulation of BADH2 in the metabolic pathway offers a promising strategy to enhance 2AP production in millets. Understanding the structure and function of BADH2 is essential for improving aroma traits, and genome editing (GE) approaches present a viable avenue for functional enhancement. In this review, we highlight the significance of 2AP and its metabolic pathways in crops and provide insights into the structural and functional features of BADH2. We mined putative BADH proteins from foxtail millet, finger millet, and sorghum using the rice OsBADH2 sequence as a reference, and analyzed their physicochemical and protein characteristics via in silico approaches. Furthermore, we discuss potential functional motif modifications of BADH2 in millets to enhance 2AP production through GE strategies. This review offers a comprehensive perspective on engineering BADH2 functional motifs to develop fragrant millet varieties. These insights could accelerate millet improvement and support the global promotion and adoption of millet-based foods.