On Feb 22, 2013, Joint Statement by the United States and Japan are announced on MOFA web site.
Should Japan participate in the TPP negotiations, all goods would be subject to negotiation, however the statement acknowledged "sensitivities" on both ends, including agricultural products for Japan and manufactured goods for the United States.
The keywords of this announcement is here:
"As the final outcome will be determined during the negotiations, it is not required to make a prior commitment to unilaterally eliminate all tariffs upon joining the TPP negotiations."
This statement follows the political commitment Prime Minister Shizo Abe made domestically in the general election in December 2012, Japanese government will be able to go forward internal procedure to formally join TPP negotiation.