Elucidating the mechanisms underlying the formation of storage roots is important for further improvement of sweetpotato. Although the process of storage root formation in sweetpotato has been extensively studied anatomically and physiologically, the genetic and molecular mechanisms remain largely unknown. Recently, extensive gene expression analysis has identified numerous genes differentially expressed between fibrous and storage roots. The results of these analyses agreed with previous anatomical and physiological observations in that genes related to starch and storage protein biosynthesis were up-regulated, and those related to lignin biosynthesis were down-regulated in the storage roots.
Also, molecular biological studies and analyses using transgenic sweetpotato plants have suggested that an expansin protein and several transcription factor genes, such as a Dof-type zinc nger protein, MADS-box proteins, and KNOXI proteins, are involved in the characteristic physiological process of storage root formation. Furthermore, ongoing whole-genome sequencing of sweetpotato and the related Ipomoea species is expected to identify genetic differences related to storage root formation. Although these studies are valuable as a first step in elucidating the critical genes and genetic network that control the formation of storage roots, further physiological, genetic, and molecular biological studies are needed to reveal the entire molecular process.