**1. Introduction**

Seed development is a unique attribute of plants providing them the privilege of perpetuating genetic information over generations by safeguarding against environmental atrocities. Physiologically, it is a combined effect of two complex developmental processes, embryo and endosperm development. In case of dicots, majority of the seed volume is formed by the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

embryo at maturity and the endosperm is consumed by the embryo during the course of seed development. The structure of monocot seed, such as rice, is different from a dicot seed by the presence of a starchy endosperm which occupies most of the space inside the seed coat and the embryo is positioned at the ventral side. Furthermore, the seed is covered entirely by the husk, which is formed by drying of the lemma and the palea. Seeds serve as the storage factories for synthesizing carbohydrates, proteins and lipid molecules, hence act as nutrition suppliers to the germinating seedling as well as to animals and humans. Rice seeds, in particular, are the major calorie providers constituting about 20% of the human nutrition worldwide [1, 2]. Therefore, it becomes imperative to understand seed development in rice to produce varieties with improved nutritional content and yield.

Seed development in rice incorporates development of the embryo and the endosperm and occurs in a systematic and sequential manner followed by desiccation and seed dormancy. The entire process of seed development in rice has been summated into five different stages from S1 to S5, categorized as 0–2, 3–4, 5–10, 11–20 and 21–29 days after pollination (DAP) seeds, respectively. Developmental period of the seed consisting of post-fertilization to middle globular embryo constitutes the first stage followed by embryo patterning and endosperm cellularization in second stage. The third stage is concerned with embryo morphogenesis, formation of a milky endosperm and initiation of endoreduplication. In the maturation phase, the milky endosperm transits from soft dough and hard dough stages in S4, and the seeds progress towards dormancy and desiccation in S5 stage [3, 4]. These developmental changes are channelized impeccably through the skillful operation of several genes and complex regulatory networks upon perception of internal and external stimuli [4–6]. Recent technological advances have facilitated the identification of genes responsible for guiding various steps of seed development. High-throughput mRNA profiling studies or transcriptomics is one such technology that has helped in deriving vital information about a myriad of molecular events that orchestrate seed development [7, 8]. Transcriptome profiling of a wide range of rice tissues, including vegetative and reproductive tissues, have proved beneficial in providing primary information about the genes expressed during seed development including their levels, patterns and molecular functions [6, 9–11]. With the aid of advanced bioinformatics platforms, transcriptome data is now being processed to derive more complex interpretations including pathways and regulatory networks that provide more complete picture of the molecular changes regulating seed development [12–15].
