CONCLUSIONS
Despite a number of comprehensive studies on the transcriptome atlas of
seed development with high spatio-temporal resolutions, definite
information about the interaction between the two economically important
tissues of embryo and endosperm is still lacking. In this study, we
successfully applied a novel comparison method based on the NB mutant,
demonstrating a direct effect of embryo on the developmental processes
of endosperm. Integrated analysis of transcriptome and metabolites
identified putative regulatory timers that coordinate the developmental
process between embryo and endosperm. The external timers for endosperm
may be hormones like GA secreted from the embryo, while the internal
timers be the T6P-SnRK1 signaling pathway that mediates carbon
allocation in endosperm. In combination with results from molecular,
physiological, and anatomical investigations, we framed a holistic and
dynamic landscape of rice seed development, and explained its
agronomical significance, in particular for the intensive systems of
rice-wheat or rice-oilseed rape double cropping. In contrast to the
quantum leap in fundamental science of genetic control of seed
development, progress on the applied science like the physiology of
grain filling and quality has apparently lagged behind. The integrative
picture of rice grain formation proposed here is of value to bridge this
knowledge gap, and will facilitate the designing of cogent strategies to
enhance rice yield and quality.