Abstract: To elucidate the functions of male sterile 2-like protein（MSLP）in citrus，the full-length cDNAs of MSLP were cloned in six typical citrus varieties using RT-PCR. Four transcripts of MSLP were identified，and only MSLP-B existed in all varieties. Structure analysis showed MSLP contained three conserved fatty acyl-CoA reductase（FAR）C terminal domains. Phylogenetic analysis suggested that MSLP-B clustered with sweet orange FAR-like protein and clementine FAR3 protein，and they had closer genetic relationship with FAR-proteins in rosaceous plant like peach，rose，sweet cherry and plum. Southern blotting showed there were 5–8 copies of MSLP in citrus. Transient expression of MSLP-B-GFP in Nicotiana benthamiana leaves indicated it functioned in cytoplasm. qRT-PCR results showed the expression of MSLP-B in floral organs of seedless Ponkan was up-regulated compared with common seedy Ponkan. Over-expression of MSLP-B in tobacco showed that the ratio of stylar length to filament length in mature flower was higher than non-transgenic tobacco. The viability of pollen grains was normal in transgenic lines. However，the number of unsaturated elliptic pollen grains increased significantly.

Key words: citrus, male sterility, male sterile 2-like protein, seedlessness