Abstract: The proteins of HL type cytoplasmic male sterility(CMS)rice pollen of YTA(male-sterile line)and YTB(maintenance line)were separated by two-dimensional electrophoresis with immobilized pH(3-10 non-linear,NL)gradients as the first dimension and SDS-PAGE as the second.The silver-stained proteins spots were analyzed using Image Master 2D software,there were about 1500 detectable spots on each 2D-gel,and about 120 spots were differentially expressed.With direct MALDI-TOF mass spectrometry analysis and protein database searching,7 protein spots out of 15 were identified.Among those proteins,there were 4 proteins were down-regulated or absent in YTA,which were a putative phosphoribosyl pyrophosphate synthase,a putative membrane-associated salt-inducible protein,a putative mitochondrial NAD⁺-dependent malic enzyme and a rice mitochondrion H⁺-transporting two-sector ATPase alpha chain respectively.It seemed reasonable to infer that the decrease or absence of those proteins in pollen might relate to the pollen sterility caused by the mitochondrial insufficient energy.While the up-regulation of the protein,mitochondrial voltage-dependent anion-selective channel(VDAC)protein,in YTA,might involve in the programmed cell death during the pollen abortion.