Seeds or grains from cereals such as rice, maize, wheat,
barley, and sorghum are the main resource for human
nutrition and animal feed throughout the world. Grains
consist of several types of tissue and their development is
a highly complicated and well-regulated developmental
process. From a nutritional aspect, the seed-storage proteins
and starch are the two main components. Accumulation
of storage starch and protein is coordinated with
cellular differentiation and development of different tissues
in the caryopsis, which is the dry, indehiscent fruit
in which the grain is formed. This suggests that understanding
of grain development and in particular the communication
between different cell types will also be
crucial for understanding grain quality in addition to
understanding regulation of starch synthetase and seedstorage
protein genes. The composition of the grain and
its quality also depends on the carbon and nitrogen
metabolism in source tissues, as well as the translocation
of photo-assimilates and amino acids to the sink tissue,
the kernels, which implicates that holistic studies on the
whole plant level are critical. Last but not least, the
molecular basis and the signaling pathways responding to
environmental factors which can have strong and adverse
effects on grain quality are far from clear yet. Large
advances have been made in understanding the molecular
and genetic basis of grain quality in rice. Seed-storage
protein genes and the genes underlying starch biosynthesis
have been cloned, and their functions in grain quality
were described. The regulation of these genes on the levels
of transcription and post-transcription, during development
and in response to environmental conditions, is yet
far from being understood. Many important cis- and
trans-acting factors have been identified. However, most
transcription regulators were identified through artificial
in vitro systems which need further confirmation with
genetic studies. Last decade many transposon and T-DNA
mutant resources have been developed which will help
understanding gene functions (Krishnan et al. 2009).