Molecular and environmental factors determining grain quality in rice

Rice among other cereals is key to food security for at least half the world population. Since the 1960s, productivity of rice has largely been improved during the G reen R evolution, which included development of new cultivars, irrigation infrastructure, new management techniques, and synthetic fertilizers and pesticides. Nowadays, scientists and breeders are more and more focused on improving the quality of rice for different purposes and markets. For instance, people in the Far East prefer sticky and soft rice, while in I ndia, a non‐sticky type is preferred. Consumers from developed countries ask mainly for grain with good cooking quality and eating characteristics, but in many developing regions, nutritional value is crucial as rice is the most consumed staple food. Grain quality is a general concept which covers many characteristics ranging from physical to biochemical and physiological properties. Starch and protein are the two main components of rice endosperm and therefore are key to quality. The knowledge of how starch and protein are synthesized, sorted, and stored in starch granules and protein bodies (PB) is important for rice breeding. Besides that, grain quality has been shown to be affected significantly by growing and environmental conditions, such as water availability, temperature, fertilizer application, drought, and salinity stresses. However, the signal transduction pathways controlling grain quality still remain largely unclear. In the following sections, we first briefly review the four main aspects of grain quality, followed by a discussion of the molecular and genetic basis of starch and seed‐storage protein biosynthesis and the effects of environmental factors. Obviously, rice grain is also an important source of mineral micronutrients, as well as important vitamins. Storage of these also plays crucial roles in grain quality and nutritional value, but we will only discuss these aspects briefly in this review.