This domain family is found in Metazoa and in Virdiplantae. Two of the family members are characterized in Arabidopsis thaliana. Swiss:O22943 and Swiss:Q9SCN0 and named STELLO1 (STL1) and STELLO2 (STL2) respectively. They are Golgi-localized proteins that can interact with CesAs (cellulose synthase A) and control cellulose quantity. In the absence of STELLO function, the spatial distribution within the Golgi, secretion and activity of the CSCs are impaired indicating a central role of the STELLO proteins in CSC assembly. Point mutations in the predicted catalytic domains of the STELLO proteins indicate that they are glycosyltransferases facing the Golgi lumen. STL homologues are present throughout the plant kingdom, but STL proteins are distinct from distantly related proteins in nematodes, fungi and molluscs [1].

1: Golgi-localized STELLO proteins regulate the assembly and trafficking of cellulose synthase complexes in Arabidopsis. Zhang Y, Nikolovski N, Sorieul M, Vellosillo T, McFarlane HE, Dupree R, Kesten C, Schneider R, Driemeier C, Lathe R, Lampugnani E, Yu X, Ivakov A, Doblin MS, Mortimer JC, Brown SP, Persson S, Dupree P; Nat Commun. 2016;7:11656. PMID:27277162