Conservation analyses
The two standard numbering schemes were used to analyze the amino acid frequencies for the two expansin domains. The domains were annotated by using hmmscan against all sequence entries of the ExED and deploying the match criteria mentioned above. Each annotated domain position was analyzed for conserved amino acids. Groups of amino acids with similar biochemical properties, such as charge or polarity, were also taken into account39,40. Conservation analyses were performed separately for each superfamily of the ExED, and additionally for EXPA, EXPB, EXLA (expansin-like A), and EXLB (expansin-like B) (Tables S3 and S4 ). An amino acid position was defined as conserved if it occurred in at least 70% of all annotated sequence entries. Conserved positions were compared with the positions in the structures of two bacterial expansins (PDB entries 4fer, chain B and 4jjo, chain A) and two plant expansins (PDB entries 1n10, chain A and 2hcz, chain X) to predict their functional relevance.