Alignment of the sequences of select RLKs belonging to the RD kinase family showing the Arg residue preceding the invariant Asp in the catalytic subdomain VI, the activation loop sequence in between the “DFG” in subdomain VII and “APE” in subdomain VIII, and the conserved Thr residue. The Gen Bank accession numbers of the sequences are: ACR4 (AB074762), AtSERK1/BAK1 (AT4G33430), SYMRK (AF492655), BRI1 (AT4G39400), ERECTA (AT2G26330), TMK1 (AT1G66150), CLV1 (AT1G75820).