It　has　been　theoretically　proposed　that　the　spin　textures　of　surface　states　in　a　topological　insulator　can　be　directly　transferred　to　graphene　by　means　of　the　proximity　effect,　which　is　very　important　for　realizing　a　two-dimensional　topological　insulator　based　on　graphene.　Here　we　report　the　anomalous　magnetotransport　properties　of　graphene　topological　insulator　Bi2Se3　heterojunctions,　which　are　sensitive　to　the　electronic.　coupling　between　graphene　and　the　topological　surface　state.　The　coupling　between　the　p(z)　orbitals　of　graphene　and　the　p　orbitals　of　the　surface　states　on　the　Bi2Se3　bottom　surface　can　be　enhanced　by　applying　a　perpendicular　negative　magnetic　field,　resulting　in　a　giant　negative　magnetoresistance　at　the　Dirac　point　up　to　about　-91%.　An　obvious　resistance　dip　in　the　transfer　curve　at　the　Dirac　point　is　also　observed　in　the　hybrid　devices,　which　is　consistent　with　theoretical　predictions　of　the　distorted　Dirac　bands　with　nontrivial　spin　textures　inherited　from　the　Bi2Se3　surface　states.