Surface recognition and appressorium penetration are critical infection processes in rice blast fungus Magnaporthe oryzae and many other plant pathogenic fungi.Various chemical and physical surface signals are known to be recognized by germ tubes to activate the Pmkl MAP kinase that is conserved in fungal pathogens for regulating appressorium formation and penetration.Recently, the MoMsb2 mucin gene was found to function as a surface sensor upstream from the Pmk1 pathway.However, it is not clear how MoMsb2 become activated and what is its relationship with other surface sensors.In this study, we found that the putative cleavage domain and transmembrane domain are essential for MoMsb2 functions.Site-directly mutagenesis was used to verify six candidate cleavage amino acid sites, and His637 was identified as the main cleavage site.Transformants without the whole cytoplasmic tail domain just had a slightly effects on appressorium formation on plastic hydrophobic surface.In addition, these transformants can lead to as many lesions as wild-type, but the size of most lesions is smaller than wildtype.Furthermore, our data showed that both transformants over expressing the whole C-terminal region of MoMsb2 with or without TM domain cant rescue defects of MoMsb2 mutant in appressorium formation and virulence.We concluded that the extracellular part of MoMsb2 may play an essential role in appressorium formation and virulence.Since MoCbp1 is one of the only two mucin genes in M.oryzae, we also generated MoCbp1 single mutant and MoMsb2 MoCbpl double mutants.The MoMsb2 MoCbp1 double mutant cant form any appressoria and was no pathogenic, indicating that Msb2 and Cbp1 may have overlapping functions in surface recognition.