Engineering purple rice for human health

Developing carotenoids-enhanced tomato fruit with multi-transgene stacking strategies

As natural dominant pigments, carotenoids and their derivatives not only contribute to fruit color and flavor quality but are regarded as phytochemicals beneficial to human health because of various bioactivities. Tomato is one of the most important vegetables as well as a main dietary source of carotenoids. So, it's of great importance to generate carotenoid-biofortified tomatoes. The carotenoid biosynthesis pathway is a network co-regulated by multiple enzymes and regulatory genes. Here, we assembled four binary constructs containing different combinations of four endogenous carotenoids metabolic-related genes, including SlORHis, SlDXS, SlPSY, and SlBHY by using a high efficiency multi-transgene stacking system and a series of fruit-specific promotors. Transgenic lines overexpression SlORHis alone, three genes (SlORHis/SlDXS/SlPSY), two genes (SlORHis/SlBHY), and all these four genes (SlORHis/SlDXS/SlPSY/SlBHY) were enriched with carotenoids to varying degrees. Notably, overexpressing SlORHis alone showed comparable effects with simultaneous overexpression of the key regulatory enzyme coding genes SlDXS, SlPSY, and SlORHis in promoting carotenoid accumulation. Downstream carotenoid derivatives zeaxanthin and violaxanthin were detected only in lines containing SlBHY. In addition, the sugar content and total antioxidant capacity of these carotenoids-enhanced tomatoes was also increased. These data provided useful information for the future developing of biofortified tomatoes with different carotenoid profiles, and confirmed a promising system for generation of nutrients biofortified tomatoes by multiple engineering genes stacking strategy.

Transcriptome Screening of Long Noncoding RNAs and Their Target Protein-Coding Genes Unmasks a Dynamic Portrait of Seed Coat Coloration Associated with Anthocyanins in Tibetan Hulless Barley

Many plants have the capability to accumulate anthocyanins for coloration, and anthocyanins are advantageous to human health. In the case of hulless barley (Hordeum vulgare L. var. nudum), investigation into the mechanism of anthocyanin formation is limited to the level of protein-coding genes (PCGs). Here, we conducted a comprehensive bioinformatics analysis to identify a total of 9414 long noncoding RNAs (lncRNAs) in the seed coats of purple and white hulless barley along a developmental gradient. Transcriptome-wide profiles of lncRNAs documented several properties, including GC content fluctuation, uneven length, a diverse range of exon numbers, and a wide variety of transcript classifications. We found that certain lncRNAs in hulless barley possess detectable sequence conservation with Hordeum vulgare and other monocots. Furthermore, both differentially expressed lncRNAs (DElncRNAs) and PCGs (DEPCGs) were concentrated in the later seed development stages. On the one hand, DElncRNAs could potentially cis-regulate DEPCGs associated with multiple metabolic pathways, including flavonoid and anthocyanin biosynthesis in the late milk and soft dough stages. On the other hand, there was an opportunity for trans-regulated lncRNAs in the color-forming module to affect seed coat color by upregulating PCGs in the anthocyanin pathway. In addition, the interweaving of hulless barley lncRNAs and diverse TFs may function in seed coat coloration. Notably, we depicted a dynamic portrait of the anthocyanin synthesis pathway containing hulless barley lncRNAs. Therefore, this work provides valuable gene resources and more insights into the molecular mechanisms underlying anthocyanin accumulation in hulless barley from the perspective of lncRNAs, which facilitate the development of molecular design breeding in crops.

Rice carotenoid biofortification and yield improvement conferred by endosperm-specific overexpression of OsGLK1

Carotenoids, indispensable isoprenoid phytonutrients, are synthesized in plastids and are known to be deficient in rice endosperm. Many studies, involving transgenic manipulations of carotenoid biosynthetic genes, have been performed to obtain carotenoid-enriched rice grains. Nuclear-encoded GOLDEN2-LIKE (GLK) transcription factors play important roles in the regulation of plastid and thylakoid grana development. Here, we show that endosperm-specific overexpression of rice GLK1 gene (OsGLK1) leads to enhanced carotenoid production, increased grain yield, but deteriorated grain quality in rice. Subsequently, we performed the bioengineering of carotenoids biosynthesis in rice endosperm by introducing other three carotenogenic genes, tHMG1, ZmPSY1, and PaCrtI, which encode the enzymes truncated 3-hydroxy-3-methylglutaryl-CoA reductase, phytoene synthase, and phytoene desaturase, respectively. Transgenic overexpression of all four genes (OsGLK1, tHMG1, ZmPSY1, and PaCrtI) driven by rice endosperm-specific promoter GluB-1 established a mini carotenoid biosynthetic pathway in the endosperm and exerted a roughly multiplicative effect on the carotenoid accumulation as compared with the overexpression of only three genes (tHMG1, ZmPSY1, and PaCrtI). In addition, the yield enhancement and quality reduction traits were also present in the transgenic rice overexpressing the selected four genes. Our results revealed that OsGLK1 confers favorable characters in rice endosperm and could help to refine strategies for the carotenoid and other plastid-synthesized micronutrient fortification in bioengineered plants.

The Potential of High-Anthocyanin Purple Rice as a Functional Ingredient in Human Health

Purple rice is recognized as a source of natural anthocyanin compounds among health-conscious consumers who employ rice as their staple food. Anthocyanin is one of the major antioxidant compounds that protect against the reactive oxygen species (ROS) that cause cellular damage in plants and animals, including humans. The physiological role of anthocyanin in plants is not fully understood, but the benefits to human health are apparent against both chronic and non-chronic diseases. This review focuses on anthocyanin synthesis and accumulation in the whole plant of purple rice, from cultivation to the processed end products. The anthocyanin content in purple rice varies due to many factors, including genotype, cultivation, and management as well as post-harvest processing. The cultivation method strongly influences anthocyanin content in rice plants; water conditions, light quantity and quality, and available nutrients in the soil are important factors, while the low stability of anthocyanins means that they can be dramatically degraded under high-temperature conditions. The application of purple rice anthocyanins has been developed in both functional food and other purposes. To maximize the benefits of purple rice to human health, understanding the factors influencing anthocyanin synthesis and accumulation during the entire process from cultivation to product development can be a path for success.

TransGene Stacking II Vector System for Plant Metabolic Engineering and Synthetic Biology

Efficient stacking of multiple genes is a critical element in metabolic engineering of complex pathways, synthetic biology, and genetic improvement of complex agronomic traits in plants. Here we present a high-efficiency multigene assembly and transformation vector system, TransGene Stacking II (TGS II), for these purposes. The operation process is described in detail, and the successful operation mainly depends on effective reagents, special Escherichia coli strains, and basic molecular biological means without other specific equipments.

Plant Synthetic Metabolic Engineering for Enhancing Crop Nutritional Quality

Nutrient deficiencies in crops are a serious threat to human health, especially for populations in poor areas. To overcome this problem, the development of crops with nutrient-enhanced traits is imperative. Biofortification of crops to improve nutritional quality helps combat nutrient deficiencies by increasing the levels of specific nutrient components. Compared with agronomic practices and conventional plant breeding, plant metabolic engineering and synthetic biology strategies are more effective and accurate in synthesizing specific micronutrients, phytonutrients, and/or bioactive components in crops. In this review, we discuss recent progress in the field of plant synthetic metabolic engineering, specifically in terms of research strategies of multigene stacking tools and engineering complex metabolic pathways, with a focus on improving traits related to micronutrients, phytonutrients, and bioactive components. Advances and innovations in plant synthetic metabolic engineering would facilitate the development of nutrient-enriched crops to meet the nutritional needs of humans.

From Golden Rice to aSTARice: Bioengineering Astaxanthin Biosynthesis in Rice Endosperm

Carotenoids are important phytonutrients with antioxidant properties, and are widely used in foods and feedstuffs as supplements. Astaxanthin, a red-colored ketocarotenoid, has strong antioxidant activity and thus can benefit human health. However, astaxanthin is not produced in most higher plants. Here we report the bioengineering of astaxanthin biosynthesis in rice endosperm by introducing four synthetic genes, sZmPSY1, sPaCrtI, sCrBKT, and sHpBHY, which encode the enzymes phytoene synthase, phytoene desaturase, β-carotene ketolase, and β-carotene hydroxylase, respectively. Transgneic overexpression of two (sZmPSY1 and sPaCrtI), three (sZmPSY1, sPaCrtI and sCrBKT), and all these four genes driven by rice endosperm-specific promoters established the carotenoid/ketocarotenoid/astaxanthin biosynthetic pathways in the endosperm and thus resulted in various types of germplasm, from the yellow-grained β-carotene-enriched Golden Rice to orange-red-grained Canthaxanthin Rice and Astaxanthin Rice, respectively. Grains of Astaxanthin Rice were enriched with astaxanthin in the endosperm and had higher antioxidant activity. These results proved that introduction of a minimal set of four transgenes enables de novo biosynthesis of astaxanthin in the rice endosperm. This work provides a successful example for synthetic biology in plants and biofortification in crops; the biofortified rice products generated by this study could be consumed as health-promoting foods and processed to produce dietary supplements.