Prospects to improve the nutritional quality of crops

Grain lysine enrichment and improved stress tolerance in rice through protein engineering

Amino acids are a major source of nourishment for people living in regions where rice is a staple food. However, rice grain is deficient in essential amino acids including lysine. The activity of the enzyme dihydrodipicolinate synthase (DHDPS) is crucial for lysine production in higher plants, but it is tightly regulated through feedback inhibition by its end product, lysine, leading to limited activity in the grain and resulting in low lysine accumulation. We identified lysine binding sites in the DHDPS enzyme and introduced key mutations to make DHDPS lysine feedback insensitive. Using in vivo analysis and functional complementation assays, we confirmed that protein engineering of the DHDPS renders it insensitive to lysine. Expression of mutated DHDPS resulted in 29% higher lysine and 15% higher protein accumulation in rice grains than in the wild type. Importantly, the lysine content in transgenic grains was maintained in cooked rice. The transgenic plants also exhibited enhanced stress tolerance along with higher antioxidant levels, improved photosynthesis, and higher grain yield compared to wild-type plants. We have shown that protein engineering of DHDPS in rice can lead to accumulation of lysine in grains and impart abiotic stress tolerance. This approach could improve health in regions with nutrient deficiencies and environmental stressors that challenge food production and human health.

Nutritional enhancement of animal feed and forage crops via genetic modification

Introducing beneficial productivity and nutritional traits into food, feed and forage crops utilising the tools of biotechnology can lead to improvements via genetic modification that cannot be achieved by traditional plant breeding. The timelines and costs are significant, and the regulatory hurdles can lead to some promising traits failing to be commercialised. These challenges mean that large commodity crops are the primary beneficiaries of biotechnology. New Zealand being primarily a grazing pastoral agricultural market and small in international terms, faces greater challenges. The species used in pastoral agriculture have relatively small seed markets and therefore limited investment for genetic improvement. The nutritional quality of feed and forages both in composition and in energy density per ha has a major influence on animal productivity and the environmental impacts of agriculture. Through government and private industry support, AgResearch has developed novel approaches to improve plant photosynthesis, energy density, and nutritional quality that has applications in crops globally. This review discusses the different challenges and solutions to improving plant nutrient density and outlines the benefits of these novel biotechnology traits in animal forage and feed crops.

Orchestrating seed storage protein and starch accumulation toward overcoming yield-quality trade-off in cereal crops

Achieving high yield and good quality in crops is essential for human food security and health. However, there is usually disharmony between yield and quality. Seed storage protein (SSP) and starch, the predominant components in cereal grains, determine yield and quality, and their coupled synthesis causes a yield-quality trade-off. Therefore, dissection of the underlying regulatory mechanism facilitates simultaneous improvement of yield and quality. Here, we summarize current findings about the synergistic molecular machinery underpinning SSP and starch synthesis in the leading staple cereal crops, including maize, rice and wheat. We further evaluate the functional conservation and differentiation of key regulators and specify feasible research approaches to identify additional regulators and expand insights. We also present major strategies to leverage resultant information for simultaneous improvement of yield and quality by molecular breeding. Finally, future perspectives on major challenges are proposed.

Sulfate transport and metabolism: strategies to improve the seed protein quality

Sulfur-containing amino acids (SAA), namely methionine, and cysteine are crucial essential amino acids (EAA) considering the dietary requirements of humans and animals. However, a few crop plants, especially legumes, are characterized with suboptimal levels of these EAA thereby limiting their nutritive value. Hence, improved comprehension of the mechanistic perspective of sulfur transport and assimilation into storage reserve, seed storage protein (SSP), is imperative. Efforts to augment the level of SAA in seed storage protein form an integral component of strategies to balance nutritive quality and quantity. In this review, we highlight the emerging trends in the sulfur biofortification approaches namely transgenics, genetic and molecular breeding, and proteomic rebalancing with sulfur nutrition. The transgenic 'push and pull strategy' could enhance sulfur capture and storage by expressing genes that function as efficient transporters, sulfate assimilatory enzymes, sulfur-rich foreign protein sinks, or by suppressing catabolic enzymes. Modern molecular breeding approaches that adopt high throughput screening strategies and machine learning algorithms are invaluable in identifying candidate genes and alleles associated with SAA content and developing improved crop varieties. Sulfur is an essential plant nutrient and its optimal uptake is crucial for seed sulfur metabolism, thereby affecting seed quality and yields through proteomic rebalance between sulfur-rich and sulfur-poor seed storage proteins.

Improving crop yield potential: Underlying biological processes and future prospects

The growing world population and global increases in the standard of living both result in an increasing demand for food, feed and other plant-derived products. In the coming years, plant-based research will be among the major drivers ensuring food security and the expansion of the bio-based economy. Crop productivity is determined by several factors, including the available physical and agricultural resources, crop management, and the resource use efficiency, quality and intrinsic yield potential of the chosen crop. This review focuses on intrinsic yield potential, since understanding its determinants and their biological basis will allow to maximize the plant's potential in food and energy production. Yield potential is determined by a variety of complex traits that integrate strictly regulated processes and their underlying gene regulatory networks. Due to this inherent complexity, numerous potential targets have been identified that could be exploited to increase crop yield. These encompass diverse metabolic and physical processes at the cellular, organ and canopy level. We present an overview of some of the distinct biological processes considered to be crucial for yield determination that could further be exploited to improve future crop productivity.