NF-YB1-regulated expression of sucrose transporters in aleurone facilitates sugar loading to rice endosperm

Cereal endosperms, which consist of an outer aleurone layer and an inner starchy endosperm, provide over 70% staple food for human [www.fao.org]. Rice endosperm development occurs in the caryopsis of a grain. During the grain filling stage, sucrose produced in photosynthetic leaves is transported to grains via the phloem [ 1, 2]. It has been proposed that sucrose, upon arrival in the caryopsis through the phloem located at the dorsal vascular bundle, is partially hydrolyzed by cell wall invertases （CINs） into glu- cose and fructose [3, 4]. Since endosperm is symplastically isolated from maternal tissues, it is assumed that these sug- ars are delivered to the endosperm actively through an ap- oplastic pathway by sugar transporters located in aleurone [5, 6]. However, the exact role of aleurone in regulating sugar transport remains unknown.