Materials and methods Dataset collectionThe amino acid sequences of Deg1 (At3g27925), Deg5 (At4g18370), and Deg8 (At5g39830.1) were collected from The Arabidopsis Information Resource database (TAIR; http://arabidopsis.org/index.jsp). The high-resolution crystal structure of Deg1 (PDB: 3QO6) protease was obtained from the Protein Data Bank (PDB; http://www. rcsb.org). Sequence alignment of Deg1, Deg5, and Deg8 was performed using ClustalW and ESPript (Thompson et al., 1994;Gouet et al., 2003).