AIADMK is contesting all 40 seats, including one in neighbouring Union Territory of Puducherry, on its own.
DMK has firmed up alliance with IUML, MMK, VCK and Puthiya Tamizhagam.
Left parties are also left with no allies after their alliance with AIADMK collapsed over sharing of seat.
In the 2009 elections, Congress, a partner in the DMK-led DPA, had contested 16 seats and won nine of them, while the front itself claimed an impressive 28 seats.
