Catalysis of the reaction: 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) + L-alanyl-tRNA(Ala) = 1,2-diacyl-sn-glycero-3-phospho-1'-(3'-O-L-alanyl)-sn-glycerol + tRNA(Ala).
alanyl phosphatidylglycerol synthetase activity