Localization of mRNAs at the subcellular level is an essential mechanism for specific protein targeting and local control of protein synthesis in both eukaryotes and bacteria. While mRNA localization is well documented in metazoans, somatic cells, and microorganisms, only a handful of well-defined mRNA localization examples have been reported in vascular plants and algae. This review summarizes the function and mechanism of mRNA localization and highlights recent studies of mRNA localization in vascular plants. While the emphasis focuses on storage protein mRNA localization in rice endosperm cells, information on targeting of RNAs to organelles (chloroplasts and mitochondria) and plasmodesmata is also discussed. WHAT IS MRNA LOCALIZATION? Localization of mRNAs was initially discovered in the 1980s, when b-actin mRNA was found to be asymmetrically distributed in ascidian eggs and embryos (Jeffery et al., 1983). This nonuniform spatial distribution pattern was later observed for maternal mRNAs in Xenopus (Rebagliati et al., 1985) and Drosophila oocytes (Frigerio et al., 1986; Berleth et al., 1988) and supported the proposal of prelocalized RNA during early development (Davidson, 1971; Kandler-Singer and Kalthoff, 1976). Subsequently, mRNA localization was observed in a variety of somatic cells such as fibroblasts (Lawrence and Singer, 1986), oligodendrocytes (Trapp et al., 1997), and neurons (Garner et al., 1988). Today, mRNA localization is prevalent in bacteria, yeast, algae, vascular plants, and metazoans and, therefore, is an ancient, universal, evolutionarily conserved mechanism. Our understanding of mRNA localization stems mainly from research in Xenopus, Drosophila, budding yeast, fungi, and structurally polarized animal cells