Unfolded protein response and storage product accumulation in rice grains

Secretory and transmembrane proteins start to synthesize and fold in the endoplasmic reticulum (ER). When the balance between protein folding demands and protein folding capability in the ER is broken, a well-conserved process known as the unfolded protein response (UPR) is induced to restore protein homeostasis. The grain quality of rice ( Oryza sativa L.), one of the most important crops that feed more than half of the world’s population, is determined by the accumulation of nutritional components, such as seed storage proteins (SSPs) and starches in the grains. Rice SSPs are synthesized in the secretory pathways of endosperms and their biosynthesis is subject to complex regulation. Here, we focus on summarizing recent advances in our understanding of the role of UPR in grain development, especially in SSP biosynthesis in rice, and provide future perspectives on unanswered questions on improving grain quality through modulating UPR in rice.