Unraveling the regulatory network of barley grain metabolism through the integrative analysis of multiomics and mQTL

Introduction

Plants accumulate a large amount of metabolites throughout their life cycle to cope with changes in the external environment and various stress responses. These metabolites not only provide guarantee for plant growth and development, but also serve as important sources of nutrients, energy, and drugs for humans^1,2. Barley (Hordeum vulgare L.) is one of the widely cultivated cereal crops worldwide, with important application value and broad research prospects, which can not only be used as food and feed, but also plays an important role in nutrition, health care, brewing and processing^{3, 4–5}. Therefore, barley is also known as “diversified crops”. In addition, according to the degree of separation between its husks and grains, it can be divided into hulled barley and hull-less (naked) barley, naked barley also known as “qingke” in Chinese or “nas” in the Qinghai Tibet Plateau region^{6, 7–8}. In recent years, barley has been increasingly recognized as a nutritious food with rich health and medicinal value due to its high content of important physiological active substances such as flavonoids and vitamins in its grains⁹. Besides, the intake of highland barley helps reduce the risk of chronic and metabolic diseases such as coronary heart disease, type II diabetes, obesity and cancer^7,10. Qingke barley shows different grains colors, such as white, black, blue and purple. Colored barley generally has higher market competitiveness due to the high levels of bioactive compounds in its grains^{11, 12–13}. Therefore, analyzing the dynamic accumulation patterns of important nutrient active substances in the development of barley grains and their genetic regulatory mechanisms is of great significance for the future utilization of barley nutritional quality.

The phenylpropanoid metabolic pathway is one of the main secondary metabolic pathways in higher plants, and its metabolites play important roles in plant growth and development as well as in interaction with the environment^14,15. Flavonoids, as an important member of the phenylpropanoid metabolism pathway, have been reported to have pharmacological activities such as antioxidant, anti-inflammatory, antibacterial, antiviral, anti-tumor, lipid-lowering and cholesterol lowering, as well as liver protection due to their unique chemical structure^{16, 17, 18, 19, 20, 21, 22, 23–24}. Therefore, they are widely used in industries such...