Sweet potato (Ipomoea batatas) is one of the largest food crops in the world. Due to its abundance of starch, sweet potato is a valuable ingredient in food derivatives, dietary supplements, and industrial raw materials. In addition, due to its ability to adapt to a wide range of harsh climate and soil conditions, sweet potato is a crop that copes well with the environmental stresses caused by climate change. However, due to the complexity of the sweet potato genome and the long breeding cycle, our ability to modify sweet potato starch is limited. In this review, we cover the recent development in sweet potato breeding, understanding of starch properties, and the progress in sweet potato genomics. We describe the applicational values of sweet potato starch in food, industrial products, and biofuel, in addition to the effects of starch properties in different industrial applications. We also explore the possibility of manipulating starch properties through biotechnological means, such as the CRISPR/Cas-based genome editing. The ability to target the genome with precision provides new opportunities for reducing breeding time, increasing yield, and optimizing the starch properties of sweet potatoes.

Echinatin and licochalcone A (LCA) are valuable chalcones preferentially accumulated in roots and rhizomes of licorice (Glycyrrhiza inflata). The licorice chalcones (licochalcones) are valued for their anti-inflammatory, antimicrobial, and antioxidant properties and have been widely used in cosmetic, pharmaceutical, and food industries. However, echinatin and LCA are accumulated in low quantities, and the biosynthesis and regulation of licochalcones have not been fully elucidated. In this study, we explored the potential of a R2R3-MYB transcription factor (TF) AtMYB12, a known regulator of flavonoid biosynthesis in Arabidopsis, for metabolic engineering of the bioactive flavonoids in G. inflata hairy roots. Overexpression of AtMYB12 in the hairy roots greatly enhanced the production of total flavonoids (threefold), echinatin (twofold), and LCA (fivefold). RNA-seq analysis of AtMYB12-overexpressing hairy roots revealed that expression of phenylpropanoid/flavonoid pathway genes, such as phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and flavanone 3’-hydroxylase (F3’H), is significantly induced compared to the control. Transient promoter activity assay indicated that AtMYB12 activates the GiCHS1 promoter in plant cells, and mutation to the MYB-binding motif in the GiCHS1 promoter abolished activation. In addition, transcriptomic analysis revealed that AtMYB12 overexpression reprograms carbohydrate metabolism likely to increase carbon flux into flavonoid biosynthesis. Further, AtMYB12 activated the biotic defense pathways possibly by activating the salicylic acid and jasmonic acid signaling, as well as by upregulating WRKY TFs. The transcriptome of AtMYB12-overexpressing hairy roots serves as a valuable source in the identification of potential candidate genes involved in LCA biosynthesis. Taken together, our findings suggest that AtMYB12 is an effective gene for metabolic engineering of valuable bioactive flavonoids in plants.

Being sessile, plants have evolved sophisticated mechanisms to balance between growth and defense to survive in the harsh environment. The transition from growth to defense is commonly achieved by factors, such as protein kinases (PKs) and transcription factors, that initiate signal transduction and regulate specialized metabolism. Plants produce an array of lineage-specific specialized metabolites for chemical defense and stress tolerance. Some of these molecules are also used by humans as drugs. However, many of these defense-responsive metabolites are toxic to plant cells and inhibitory to growth and development. Plants have, thus, evolved complex regulatory networks to balance the accumulation of the toxic metabolites. Perception of external stimuli is a vital part of the regulatory network. Protein kinase-mediated signaling activates a series of defense responses by phosphorylating the target proteins and translating the stimulus into downstream cellular signaling. As biosynthesis of specialized metabolites is triggered when plants perceive stimuli, a possible connection between PKs and specialized metabolism is well recognized. However, the roles of PKs in plant specialized metabolism have not received much attention until recently. Here, we summarize the recent advances in understanding PKs in plant specialized metabolism. We aim to highlight how the stimulatory signals are transduced, leading to the biosynthesis of corresponding metabolites. We discuss the post-translational regulation of specialized metabolism and provide insights into the mechanisms by which plants respond to the external signals. In addition, we propose possible strategies to increase the production of plant specialized metabolites in biotechnological applications using PKs.