To feed the world′s growing population, increasing the yield of crops is not the only important factor, improving crop quality is also important, and it presents a significant challenge. Among the important crops, horticultural crops (particularly fruits and vegetables) provide numerous health compounds, such as vitamins, antioxidants, and amino acids. Essential amino acids are those that cannot be produced by the organism and, therefore, must be obtained from diet, particularly from meat, eggs, and milk, as well as a variety of plants. Extensive efforts have been devoted to increasing the levels of essential amino acids in plants. Yet, these efforts have been met with very little success due to the limited genetic resources for plant breeding and because high essential amino acid content is generally accompanied by limited plant growth. With a deep understanding of the biosynthetic pathways of essential amino acids and their interactions with the regulatory networks in plants, it should be possible to use genetic engineering to improve the essential amino acid content of horticultural plants, rendering these plants more nutritionally favorable crops. In the present report, we describe the recent advances in the enhancement of essential amino acids in horticultural plants and possible future directions towards their bio-fortification.

Anthocyanins are the main pigments in flowers and fruits. These pigments are responsible for the red, red-purple, violet, and purple color in plants, and act as insect and animal attractants. In this study, phenotypic analysis of the purple flower color in eggplant indicated that the flower color is controlled by a single dominant gene, FAS. Using an F₂ mapping population derived from a cross between purple-flowered ‘Blacknite’ and white-flowered ‘Small Round’, Flower Anthocyanidin Synthase (FAS) was fine mapped to an approximately 165.6-kb region between InDel marker Indel8-11 and Cleaved Amplified Polymorphic Sequences (CAPS) marker Efc8-32 on Chromosome 8. On the basis of bioinformatic analysis, 29 genes were subsequently located in the FAS target region, among which were two potential Anthocyanidin Synthase (ANS) gene candidates. Allelic sequence comparison results showed that one ANS gene (Sme2.5_01638.1_g00003.1) was conserved in promoter and coding sequences without any nucleotide change between parents, whereas four single-nucleotide polymorphisms were detected in another ANS gene (Sme2.5_01638.1_g00005.1). Crucially, a single base pair deletion at site 438 resulted in premature termination of FAS, leading to the loss of anthocyanin accumulation. In addition, FAS displayed strong expression in purple flowers compared with white flowers and other tissues. Collectively, our results indicate that Sme2.5_01638.1_g00005.1 is a good candidate gene for FAS, which controls anthocyanidin synthase in eggplant flowers. The present study provides information for further potential facilitate genetic engineering for improvement of anthocyanin levels in plants.

Ralstonia solanacearum is a soil-borne, plant xylem-infecting pathogen that causes the devastating bacterial wilt (BW) disease in a number of plant species. In the present study, two R. solanacearum strains with different degrees of aggressiveness―namely RsH (pathogenic to Hawaii 7996, a tomato cultivar resistant against most strains) and RsM (non-pathogenic to Hawaii 7996) were identified. Phylogenetic analysis revealed that both RsM and RsH belonged to phylotype I. To further elucidate the underlying mechanism of the different pathotypes between the two strains, we performed a comparative proteomics study on RsM and RsH in rich and minimal media to identify the change in the level of protein abundance. In total, 24 differential proteins were identified, with four clusters in terms of protein abundance. Further bioinformatics exploration allowed us to classify these proteins into five functional groups. Notably, the pathogenesis of RsM and RsH was particularly characterized by a pronounced difference in the abundance of virulence- and metabolism-related proteins, such as UDP-N-acetylglucosamine 2-epimerase (epsC) and isocitrate lyase (ICL), which were more abundant in the high pathogenicity strain RsH. Thus, we propose that the differences in pathogenicity between RsM and RsH can possibly be partially explained by differences in extracellular polysaccharide (EPS) and glyoxylate metabolism-related proteins.