Arabidopsis SERK family contains five members: AtSERK1, AtSERK2 , AtSERK3 (BAK1) , AtSERK4 (BKK1) and AtSERK5. SERK5 might not be functional due to a natural point mutation at a highly conserved "RD" motif. All other SERKs , SERK1 to SERK4, are involved in at least four distinct signaling pathways. Previous studies indicated the function of SERK1 and SERK2 in microsporgenesis; SERK1, SERK2, SERK3 and SERK4 in BR signaling pathway; SERK1, SERK2, SERK3 and SERK4 in cell death control pathway; and SERK3 in disease resistance pathway. More importantly, the multiple SERK knockout mutant phenotypes support the essential role of SERKs in BR signaling. In our model, it is hypothesized although SERKs play redundant role to each other, some SERKs play major roles in certain pathways. SERK1 and SERK2 play major role in regulating microsporgenesis; SERK1 and SERK3 in BR signaling pathway; SERK3 and SERK4 in cell death control pathway.