In order to further the understanding of the molecular mechanism of the biological nitrogen fixation, we predicted and
analyzed the non-classical secreted proteins of Rhizobium etli CFN42 by the softwares of SecretomeP2.0 and SignalP4.1. The results
showed that 596 of the 5 963 proteins in CFN42 were non-classical secreted proteins, nearly accounting for 10% of the total number,
mainly including substrates transport, virulence infection, and material metabolism etc. We identified type I, III, IV secretion systems
among the proteins which were functional annotated, the proteins played an important role in infection and the development of the root
nodules. We also found Tad, Cupin, OmPA and CsbD domains by SMART software within the hypothetical proteins, these domaincontaining
non-classical secreted proteins may participate in the host specificity ofrhizobium. In brief, non-classical proteins play a
key role in rhizobium-legume nitrogen fixation system.